Scurry County Research Articles

Surface subsidence and uplift resulting from well interventions modeled with coupled analytical solutions: Application to Groningen gas extraction (Netherlands) and CO2-EOR in the Kelly-Snyder oil field (West Texas)

This study presents a novel analytical model for history-matching the observed subsidence and/or uplift due to, respectively, fluid extraction from – or injection into – the pore space of subsurface reservoirs. Development of the model was prompted by the need to have a fast evaluation tool to support the various exploitation modes of subsurface reservoirs, either in fluid extraction projects (hydrocarbons, aquifers, geothermal fields) or in fluid storage projects (waste water, natural gas, hydrogen, and CO2-sequestration). The model proposed here is a novel analytical solution method obtained by coupling the vertical strain changes in a reservoir due to changes in reservoir pressure with a buckling plate model for the overburden. After a brief review of state-of-the-art (numerical and analytical tools), the coupled reservoir pressure change and overburden buckling model (in brief: pressure change-buckling model) is presented. Subsequently, the coupled pressure change-buckling model is applied in two case studies. The first case study history-matches the subsidence of the Groningen Field (Netherlands) over the period 1963–2020, due to the pressure depletion caused by natural gas extraction. The second case study applies the model to history-match the uplift history above an oil field in Scurry County (West Texas) over the period 2007–2011, due to net fluid injection related to enhanced oil recovery (EOR) activities. Separately, in addition to history-matching applications the coupled pressure change-buckling model can also be applied in forward modeling mode to predict the surface response of future operations involving pressure changes in subsurface reservoirs.

Guest Editorial: Why Should SPE Members Be Interested in Carbon Capture and Storage?

Guest editorial As chairperson of the SPE Carbon Capture Utilization and Storage (CCUS) Technical Section, I have frequently seen and heard the debate about CO2 and climate change at conferences, meetings, and in SPE Connect forums, often very vigorous, deep into the nuts and bolts of climate science, and with passionate discussions both pro and con. From a purely cynical point of view, I could make the argument that the debate is already over, as it is largely political, it doesn’t matter what we think, we are stuck with results that can significantly impact our industries, and we should do what we can to minimize the damage. However, I prefer to look at this more as an opportunity, a way to advance our social license, and as a series of technical issues that members of SPE are uniquely qualified to address. Since the first commercial CO2 project in Scurry County, Texas, in 1972, more than 150 additional CO2 EOR projects have been put in place worldwide. These projects initially depended on natural CO2 and were located near three large natural CO2 resources: McElmo Dome in Colorado, Bravo Dome in New Mexico, and Jackson Dome in Mississippi. More than 100 current CO2 EOR projects are located in the Permian Basin and Gulf Coast as a result. These projects were not initiated to save the planet or to sequester CO2; they were created by brilliant engineers and scientists trying to squeeze additional resources from declining reservoirs, and they continued because they were economical and extended the lives of fields. CO2 EOR in miscible or near-miscible floods can revitalize mature fields, with a typical tertiary response on the order of the secondary recovery efforts in both duration and volumes. In the past, projects have been limited by chemistry, CO2 supply, and infrastructure. According to a report by the US Bureau of Ocean Energy Management, only about 3–4% of potential US CO2 EOR sites—that is, those with proper pressure, temperature, and permeability for miscible flooding—are currently under flood. The remaining sites are awaiting available CO2, and, perhaps more importantly, favorable economics compared to other investment opportunities, such as unconventionals, where Permian shale oil is being produced for as low as $25 per barrel. Over 1 Bcf of natural CO2 is injected into the Permian Basin every day, and estimates are that between 800 million and 1 billion metric tons of CO2 have been stored during the past 45 years of CO2 EOR development in the region, more or less incidentally to the primary goal of producing incremental oil. This is very significant, because you are looking at numbers, which are on at least the same order of magnitude that the Paris Climate Agreement says we need to store over the next 20 years, and it has been done voluntarily, with existing technology, and with many more fields available for potential development.

Early Pleistocene leporids (Mammalia, Lagomorpha) of Roland Springs Ranch Locality 1 and the rise of North American Quaternary leporines

Roland Springs Ranch Locality 1 (RSR-1) is an early Pleistocene vertebrate faunal locality on the Rolling Plains of Scurry County, Texas. Leporid remains are common among material recovered from ongoing, systematic excavations at RSR-1. The size and morphology of collected lower third premolars were utilized to identify the leporid taxa present at RSR-1. The resulting sample assemblage is unique in composition, including: Hypolagus gidleyi, Hypolagus spp. (small form), Notolagus lepusculus, Nekrolagus progressus (including forms with the Lepus pattern), and Aztlanolagus agilis. The biochronology of such a combination of taxa indicates placement near the boundary between the early and late subdivisions of the Blancan Land Mammal Age, generally consistent with the current interpretation of RSR-1.The RSR-1 sample is considered against the backdrop of Neogene-Quaternary faunal turnover that included the extinction of the Archaeolaginae and radiation within the extant subfamily, Leporinae. Leporid abundance during the late Pliocene-early Pleistocene (Blancan Land Mammal Age) of North America marks peak species richness for the rabbit family. Late Miocene-early Pleistocene changes in climate and grassland composition and structure in North America coincide with this pivotal period of leporid natural history. Environmental shifts potentially created a period of expanded physical heterogeneity and niche diversification that provided the ecological conditions for archaeolagines, Blancan leporines, and emerging derived, modern type (Lepus pattern) leporines to widely coexist. The Lepus pattern of extant cottontails and jackrabbits, is hypothesized as a competitive advantage initiated by grassland change and particularly suited for the arid and open Quaternary Great Plains.

InSAR monitoring of ground deformation due to CO2 injection at an enhanced oil recovery site, West Texas

Interferometric synthetic aperture radar (InSAR) measurements have been used to measure ground deformation associated with fluid injection/production at an enhanced oil recovery (EOR) field in Scurry County, West Texas. 100 million tons (Mt) of supercritical CO2 have been sequestered here since 1972, of which about half has been sequestered since 2004. InSAR data show surface uplift up to 10cm in the field between January 2007 and March 2011. We evaluated data concerning injection and production of CO2, water, oil and hydrocarbon gas from 2004 to 2011 to investigate causes of the observed uplift. An analytical model is used to calculate reservoir pressure change and surface displacement. Our simulations show up to 10MPa pressure buildup in the reservoir over four years of net injection and production. Surface displacement predictions agree well with the InSAR observations. Water injection alone cannot explain the 2007–2011 surface uplift because the net injected water (∼1Mt) is negligible compared to the net injected CO2 (∼24Mt). The predicted total pressure buildup (up to 10MPa) consists of net CO2 injection (up to 12MPa), net water injection (up to 2MPa), and oil and gas production (up to −0.4MPa). Hence, observed ground uplift was mainly caused by CO2 injection.

Carbon Capture and Sequestration: A Potential "Win-Win" for the Oil Industry and the Public

Public Policy Focus - The status of carbon capture and sequestration. In 1972, the first commercial carbon dioxide (CO2) flood project in the world began with the injection of CO2 into the Scurry Area Canyon Reef Operators Committee (SACROC) unit in the Permian Basin in Scurry County, Texas. The goal was simple: To arrest declining oil production and recover bypassed reserves. Today, nearly 40 years later, CO2 injection is being considered on a much wider scale, and for a different purpose altogether: To help arrest an increase in the average surface temperature of the planet. CO2, among other gases such as methane and nitrous oxide, is a “greenhouse gas,” a gas that traps heat in the Earth’s atmosphere by absorbing and emitting radiation within the thermal infrared range, causing a greenhouselike warming effect. The presence of greenhouse gases in Earth’s atmosphere is vital, for without them, Earth’s surface would be on average about 59°F colder than at present. CO2 is also a key ingredient that nourishes plant life through photosynthesis.

Assessing risk to fresh water resources from long term CO2 injection–laboratory and field studies

Abstract In developing a site for geologic sequestration, one must assess potential consequences of failure to adequately contain injected carbon dioxide (CO2). Upward migration of CO2 or displacement of saline water because of increased pressure might impact protected water resources 100s to 1000s of meters above a sequestration interval. Questions posed are: (1) Can changes in chemistry of fresh water aquifers provide evidence of CO2 leakage from deep injection/sequestration reservoirs containing brine and or hydrocarbons? (2) What parameters can we use to assess potential impacts to water quality? (3) If CO2 leakage to freshwater aquifers occurs, will groundwater quality be degraded and if so, over what time period? Modeling and reaction experiments plus known occurrences of naturally CO2-charged potable water show that the common chemical reaction products from dissolution of CO2 into freshwater include rapid buffering of acidity by dissolution of calcite and slower equilibrium by reaction with clays and feldspars. Results from a series of laboratory batch reactions of CO2 with diverse aquifer rocks show geochemical response within hours to days after introduction of CO2. Results included decreased pH and increased concentrations of cations in CO2 experimental runs relative to control runs using argon (Ar). Some cation (Ba, Ca, Fe, Mg, Mn, and Sr) concentrations increased over and an order of magnitude during CO2 runs. Results are aquifer dependant in that experimental vessels containing different aquifer rocks showed different magnitudes of increase in cation concentrations. Field studies designed to improve understanding of risk to fresh water are underway in the vicinity of (1) SACROC oilfield in Scurry County, Texas, USA where CO2 has been injected for enhanced oil recovery (EOR) since 1972 and (2) the Cranfield unit in Adams County, Mississippi, USA where CO2 EOR is currently underway. Both field studies are funded by the U.S. Department of Energy (DOE) regional carbon sequestration partnership programs and industrial sponsors. Preliminary results of groundwater monitoring are currently available for the SACROC field study where researchers investigated 68 water wells and one spring during five field excursions between June 2006 and July 2008. Results to date show no trend of preferential degradation below drinking water standards in areas of CO2 injection (inside SACROC) as compared to areas outside of the SACROC oil field.

Clustering/Geostatistical/Evolutionary Approach for 3D Reservoir Characterization and Assisted History Matching in a Complex Carbonate Reservoir

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 113978, "Integrated Clustering/Geostatistical/Evolutionary Strategies Approach for 3D Reservoir Characterization and Assisted History Matching in a Complex Carbonate Reservoir, SACROC Unit, Permian Basin," by R. Gonzalez, SPE, K. Schepers, SPE, and S.R. Reeves, SPE, Advanced Resources International; E. Eslinger, SPE, Eric Geoscience and College of Saint Rose; and T. Back, NuTech Solutions, prepared for the 2008 SPE Improved Oil Recovery Symposium, Tulsa, 19–23 April. The paper has not been peer reviewed. An integrated methodology combining clustering-analysis techniques, geostatistical methods, and evolutionary-strategy technologies was developed and applied to a study area of the SACROC Unit. Clustering methods were applied to well logs and core data (with high vertical resolution for many wells) to predict porosity, permeability, and rock type. Geostatistics was applied to extend the characterization into the interwell area. Evolutionary strategies were used to refine the characterization to match historical production performance. Introduction Initially, a two-step soft-computing procedure was developed to generate core-scale porosity and permeability profiles at well locations where no core data existed. The approach applied clustering methods, based on maximum-likelihood principles, to well-log and core data for lithology interpretation, reservoir-quality characterization, and prediction of "core" parameter profiles, with high vertical resolution for many wells. This procedure enabled populating any well location with core-scale estimates of porosity and permeability and rock types, facilitating direct application of geostatistical techniques to build 3D reservoir models. Geostatistical methods then were applied to the resulting data set, and 3D spatial models of variability for clusters, porosity, and permeability were used to generate reservoir representations of porosity and permeability for flow-simulation purposes. Finally, a computer-assisted history matching by applying evolutionary-strategy technologies was used to history match the production performance of a selected subregion in the unit. The SACROC Unit comprises most of the Kelly-Snyder field and part of the Diamond "M" field in Scurry County, Texas. The unit is developed in Pennsylvanian-age reef carbonates of the Cisco and Canyon formations, with productive carbonates in both formations. The productive interval is composed mainly of limestone, although minor amounts of anh-drite, chert, sandstone, and shale can be found locally. Dolostone is rare to nonexistent. The overlying Wolfcamp shale constitutes a natural top and lateral seal. Toward the east and west boundaries, the Cisco/Canyon productive carbonate interval narrows and drops below the regional oil/water contact. Carbonate accumulations present extremely complex geometries and steep sides.

Smart-Well Technology at the SACROC CO2 EOR Project

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 100117, "Application of Smart- Well Technology to the SACROC CO2 EOR Project: A Case Study," by J. Brnak, SPE, Kinder Morgan Production Company, and B. Petrich and M.R. Konopczynski, SPE, WellDynamics, prepared for the 2006 SPE/DOE Symposium on Improved Oil Recovery, Tulsa, 22-26 April. Application of smart-field technologies to the SACROC Unit carbon dioxide enhanced oil recovery (CO2-EOR) project in Scurry County, Texas, was studied. A five-well pilot project in early 2005 demonstrated the ability of intelligent-well downhole flow-control valves to restrict or isolate the production of CO2 from breakthrough zones in production wells and to control the distribution of CO2 injection in injection wells. The objective is to reduce unnecessary cycling of CO2 between injectors and producers, improve sweep efficiency, increase oil production, and improve ultimate oil-reserves recovery. This is done with cost-effective, fit-for-purpose intelligent-well systems. SACROC Field The SACROC Unit in Scurry County, Texas, is the seventh largest oil field onshore in North America, with 2.8 billion bbl of original oil in place. Its main producing formation is the Canyon Reef, a Pennsylvanian-aged limestone carbonate and part of a reef complex called the Horseshoe Atoll. It is a highly heterogeneous formation. Permeability within a single well can range from less than 1 md to hundreds of millidarcies. Likewise, porosity can vary drastically. Net and gross thickness can change significantly over short distances. However, average reservoir properties are as follows.Depth = 6,700 ft.Thickness = 259 ft.Porosity = 7.6%.Permeability = 19.4 md. SACROC CO2 EOR Project The SACROC Unit was discovered in 1948 as the Kelly-Snyder field. The field produced under primary depletion with solution-gas expansion as the main drive mechanism. Reservoir pressure declined rapidly, and in 1952, the Kelly-Snyder and Diamond M fields were unitized. In 1954, the operator implemented a crestal waterflood in which water was injected along the center (the spine) of the field. In 1972, CO2 injection was initiated. With limited CO2 supply, the oil-production response to CO2 injection was limited. During water and CO2 flooding, H2S was introduced to the reservoir from sources outside the unit. As shown in Fig. 1, shortly after CO2 injection was initiated, the unit's oil production peaked with rates exceeding 200,000 BOPD. During the following decline, several projects were attempted to halt the decline, but they had little effect. In 1995, a CO2-flood pilot consisting of five-spot patterns was started. This pilot used large CO2-injection volumes at miscible conditions, and the decline of the unit's oil production was halted. In 2001, project acreage under CO2 flooding began to expand rapidly. In response, oil production increased to more than 31,000 BOPD.

Wanted: Historic County Jails of Texas (review)

Reviewed by: Wanted: Historic County Jails of Texas Dan K. Utley Wanted: Historic County Jails of Texas. By Ed Blackburn Jr. (College Station: Texas A&M University Press, 2006. Pp. 424. Preface, maps, illustrations, appendices, bibliography, index. ISBN 1585443085. $39.95, cloth.) Retired Houston physician Edward Blackburn Jr. traveled to all 254 counties of the state to compile his recent detailed inventory of Texas jails. Focusing on the century from 1840 to 1940, primarily to include the early building types and to cover what is considered by many architectural historians the heyday of public building construction in the late nineteenth and early twentieth centuries, he provides the reader with historical background on the counties through general sources, such as newspapers, The New Handbook of Texas, the Texas Almanac, and county history books. In addition, his interviews with local officials and historians, as well as newspaper editors and writers, serve to document both the history and the lore surrounding the early law enforcement centers. Blackburn's work is a worthy companion to other public building inventories, such as The Texas Courthouse, by June Rayfield Welch and J. Larry Nance (GLA Press, 1971), and The Courthouses of Texas: A Guide, by Mavis P. Kelsey and Donald H. Dyal (Texas A&M University Press, 1993). It also provides important supplement to broader architectural studies, most notably Willard Robinson's seminal work, The People's Architecture: Texas Courthouses, Jails, and Municipal Buildings (Texas State Historical Association, 1983). [End Page 418] As the first comprehensive and readily accessible survey of the state's historic jails, Blackburn's book will serve as a necessary reference tool for inquiries on a wide variety of historical topics, from architecture and criminology to local government planning. It will also hopefully serve as a point of departure for more focused analytical studies on related topics, including: architects like Eugene T. Heiner and brothers Oscar and F. E. Ruffini; contractors like the firm of Martin, Byrnes, and Johnson; and jail manufacturers, particularly Pauly Jail Building and Manufacturing, Diebold Safe and Lock, and Southern Steel Company. Readers will appreciate the high-quality photographs that illustrate the brief histories. Drawn from archival collections, as well as the author's personal site visits, they depict a wide range of form and design, from the stately 1887 Ellis County Jail to the virtually unadorned Motley County Jail of 1891. Of particular interest because of their obvious architectural statements are the fortress-like designs of the twin-towered 1912 Scurry County Jail, the smaller 1881 Bandera County Jail, and the grand 1896 Austin County Jail. Such county castles were once common across the state, but those that remain, for the most part, now serve other purposes, including museums and visitor centers. Rarely, however, are their unique histories adequately interpreted for the public. Broader societal concerns such as national security, economics, and human rights now drive jailhouse design, resulting in structures with less emphasis on aesthetics. While such change is inevitable and necessary, it is also, on a number of planes, regrettable. Fortunately, though, for those seeking more insights about a remarkable era of public architecture, Edward A. Blackburn Jr. has provided a suitable, entertaining, and enlightening means of exploring the state's landmarks of law. Dan K. Utley Texas Historical Commission Copyright © 2007 The Texas State Historical Association

Production of CO2 From a Reservoir - A New Concept

Summary Very large reservoirs of approximately 985 CO2 have been discovered in southwestern Colorado. These reservoirs have pressures up to 2,700 psi (18.70 Mpa) and temperatures to 171°F (77°C). Wells are capable of flowing more than 10 MMcf/D (0.28×106 m3/d) CO2. The CO2 flows to the surface at pressures and temperatures below the critical and, therefore, in two-phase flow. For convenient handling, the CO2 must be heated to form a single-phase gas before it is transported, dehydrated, and compressed. This paper discusses a patented procedure for downhole pressuring followed by the production and processing of CO2 under continuous supercritical conditions. It also describes a field test of the procedure and the test results. The process is dependent on the properties of CO2 under continuous high pressure and even at high temperature, which approach those of a liquid. Thus, the CO2 can be produced by conventional pumping operations. The process appears applicable to production from any CO2 reservoir containing a fluid above its critical pressure. The results of the field test were very close to those anticipated by calculation. Introduction For at least the past 15 years, interest in CO2 as a tertiary recovery technique has grown. To date, most of the CO2 has been salvaged off-gas from sweetening operations in gasoline plants. This gas generally contained 10% or more extraneous gases, including nitrogen, hydrogen sulfide, and methane. The principal advantage of CO2 in tertiary recovery is its miscibility, under certain conditions of pressure and temperature, with the reservoir liquids. The first reservoir where large volumes of CO2 have been injected is the Canyon Reef reservoir of the SACROC unit in Scurry County, TX. The procedure and results of that operation are well documented.1–4 It was established that CO2 of less than approximately 87.5% pure would not be miscible with the reservoir liquids under the Canyon Reef conditions. The purity required varies from field to field because of differences in temperature, pressure, and reservoir liquids characteristics. Many fields in west Texas are reported candidates for CO2 flooding; however, some are at lower pressures than the Canyon Reef, and some can be expected to require higher purity of CO2 than 87.5%. Higher purity CO2 is miscible with reservoir fluids at considerably lower pressure. Fig. 1 shows the approximate conditions for miscibility of 87.5% pure CO2 with produced oil from various reservoirs as they existed in 1966. Reservoir pressures have decreased in some of these reservoirs because of fluid withdrawals; others have increased because of pressure maintenance. Therefore, it is fortunate that approximately 98% pure CO2 has become available in large volumes in the McElmo field in southwestern Colorado and in other areas.5 The peculiarities of CO2, particularly the characteristic that pure CO2 exists as a two-phase fluid at ambient temperature and pressures up to 1,080 psi (7.44 MPa), make it difficult to handle at the flowing conditions of the McElmo field. Consequently, the process of pumping the supercritical CO2 with a multistage centrifugal pump was conceived.6 The procedure has been tested in the field and has proved successful.

Performance Review of a Large-Scale CO2-WAG Enhanced Recovery Project, SACROC Unit Kelly-Snyder Field

Introduction This paper reviews the performance of the CO2-WAG (water-alternating-gas) project conducted at the SACROC (Scurry Area Canyon Reef Operators Committee) Unit since early 1972. Numerous papers published previously describe in great detail the reservoir, previously describe in great detail the reservoir, the CO2 displacement process, the transmission of CO2 to the field, the mechanics of the operation of the project, a progress report through 1975, and other matters. Since detailed descriptions are available of reservoir characteristics, field history before the inception of the CO2 project, planning and design, and facilities installations, these subjects will be reviewed only briefly here. The performance of CO2 project itself since it began in J an. 1972 is emphasized. project itself since it began in J an. 1972 is emphasized. Kelly-Snyder Field, located in Scurry County, TX, is the major unitized field among four continguous fields along the 35- x 5-mile (56.3- x 8.05-km) Canyon Reef formation (Fig. 1). Reservoir and fluid properties are summarized in Table 1.Estimated original oil in place in the SACROC Unit area, based on a volumetric determination, was 2.73 billion STB (434 Mm3). This volume was used for the evaluation and design of the CO2 miscible flood and for early estimates of incremental oil recovery resulting from CO2 processing.In 1973, Chevron Oil Co., SACROC Unit operator conducted a 24-year history match of more than 1,500 wells in Kelly-Snyder Field using a two-dimensional black-oil simulator. On the basis of this study, the estimated original oil in place in the SACROC Unit area was reduced to 2.113 billion STB (335.9 Mm3). History of Kelly-Snyder Field and the SACROC Unit Before the CO2-WAG Project Project The reservoir was discovered in Nov. 1948. Subsequent development was rapid and essentially complete by Nov. 1951 when 1671 producing wells had been drilled. The production and injection history of the field is shown production and injection history of the field is shown in Fig. 2.Early production performance indicated that solution gas drive was the primary producing mechanism and that a pressure maintenance program would be required to prevent excessive loss of reserves. To improve recovery prevent excessive loss of reserves. To improve recovery the operators and royalty owners of Kelly-Snyder Field agreed to unitize to begin pressure maintenance. In 1953, the Texas Railroad Commission approved formation of the SACROC Unit.Water injection into a unique pattern involving 72 center-line injectors began Sept. 1954. Because of increased oil demand and resulting higher allowables, injection capacity had to be added beginning in 1969. During 1969-71, 72 additional wells were converted to injection service, resulting in a total of 144 center-line injectors. Operational of this center-line injection system continues presently. JPT p. 217

Early Blancan Mammals of the Beck Ranch Local Fauna of Texas

The Beck Ranch local fauna was recovered from 65 tons of sand and clay sediments from a quagmire in Scurry County, Texas. Of the 58 taxa identified, members of the genera Perognathus, Peromyscus, Nasua and Spilogale (?) are described as new species; Lasionycteris and Nasua are recorded from the Blancan age of North America for the first time; and the characters of Brachyopsigale dubius Hibbard are reassessed. The Beck Ranch local fauna is rich in small forms but larger mammals, other than Nannippus beckensis , are rare. The local fauna is thought to be younger than the Fox Canyon local fauna of Kansas, but slightly older than the Rexroad local fauna of Kansas, the Benson local fauna of Arizona, and the Blanco local fauna of Texas.

Compressibility Factors for CO2-Methane Mixtures

Compressibility factors from a high-ratio CO2-natural gas mixture are compared with other experimental data and values calculated using two correlations. Discussion includes the use of these factors in monitoring reservoir performance for the SACROC Unit CO2 injection project. Introduction The SACROC Unit CO2 injection project in Scurry County, Tex., required transporting 200 Mcf/D of CO2 for 200 miles. A feasibility study of the mode of transportation resulted in selection of a "supercritical-pressure-state" pipeline system. A study was made of available data on compressibility (z) factors for CO2-natural gas at supercritical pressures, as well as of two engineering calculation methods. This study indicated that the z factors should be measured rather than taken from published information. This paper compares our measured compressibility factors with calculated and published compressibility data, and describes applications of z factors to the various phases of the SACROC Unit CO2 injection project. phases of the SACROC Unit CO2 injection project. Experimental PVT Data There were two reasons for measuring z factors rather than relying on published information:Reamer et al.'s data for the CO2-methane system did not include C2+, which is contained in the pipeline gas.For engineering purposes, corresponding-state and equation-of-state calculation methods are not accurate enough near the critical point. CO2 pipeline design conditions include the critical point. Our measurements were made in a visual PVT cell using the CO2-natural gas mixture described in Table 1. Conditions ranged from 680 to 3,001 psia and 49 to 120 degrees F. Tables 2 and 3 and Fig. 1 show the experimental results along with the calculated values and Reamer et al.'s data. Experimental Method The gas used for the compressibility-factor measurements was prepared from pure compounds. It was analyzed by determining the CO2 in an Orsat apparatus (thus removing the CO2) and chromatographing the re-reminder of the gas. The liquid-vapor, two-phase boundary of the gas was estimated, and the gas pressure was kept above the cricondenbar to insure single-phase transfer from a storage vessel to the visual PVT cell. In the visual cell, the pressure was decreased in steps and the volume was measured at each step. This pressure-volume relation was determined at 49, 70, 90, and pressure-volume relation was determined at 49, 70, 90, and 120 degrees F. At 49 and 70 degrees F we observed bubble points and a dew point. Compressibility factors were points and a dew point. Compressibility factors were calculated from the pressure, volume, and temperature values (z = pV/RT). Experimental Results Table 1 shows the analysis of the gas used, along with the measured specific gravity and volumetric expansion values. Table 2 shows the measured z factors for the four temperatures. These data are plotted in Fig. 2 with the observed bubble and dew points. JPT P. 81

Biofacies and Development and Differential Occlusion of Porosity in A Lower Cretaceous (Edwards) Reef

ABSTRACT An Edwards reef, exposed in a large quarry in Scurry County, Texas, exhibits the following biofacies, outward from the reef core: 1) caprinid - Chondrodonta zone (reef core), 2) Eoradiolites - Chondrodonta zone (upper forereef), 3) Toucasia - Eoradiolites - Chondrodonta zone (middle forereef), 4) Cladophyllia zone (lower forereef). Beyond the forereef and below the reef are tabular biostromes in which Eoradiolites, Toucasia, Chondrodonta and Cladophyllia are dominant. The Edwards reef was subaerially exposed soon after deposition, and stabilization of carbonate mineralogy, lithification, solution, of aragonite fossils and differential cementation occurred in a fresh water diagenetic environment. Microcavernous porosity developed in the upper Edwards from solution of aragonitic caprinid and corm shells of the reef core. Adjacent to large caprinid molds former body cavities of Eoradiolites are filled by coarse calcispar cement which initiated as overgrowths on large crystals of inverted (from aragonite) calcite of the inner shell layer. Primary porosity (body cavities of calcitic pelecypods) became occluded by calcite cement, while secondary porosity (molds of aragonitic fossils) was preserved. A sharp boundary, representing a paleo-groundwater table, separates the upper paleovadose zone of microcavernous porosity from a lower paleophreatic zone wherein all former voids, including caprinid molds, became occluded by calcispar cement. A heavy concentration of vadose internal sediment terminates at the palco-groundwater table. Coarse aggrading recrystallization of micrite matrix to pseudospar is well developed in the paleophreatic zone, but is lacking in the paleovadose zone. Differential porosity occlusion was largely controlled by vadose-phreatic groundwater dynamics.

Reservoir Description by Simulation at SACROC - A Case History

To determine areal distributions of pore volume and transmissibility in an effort to control a large CO2-assisted recovery project, a 24-year history match of more than 1,500 wells was conducted with a two-dimensional, black-oil simulator. A good quantitative match resulted, which provided the necessary parameter distributions. Subsequent performance has largely supported the results of the study. Introduction The Canyon Reef reservoir in Scurry County, Tex., is about 25 miles long and from 4 to 7 miles wide. It is the largest of 15 news that lie along the eastern flank of the giant Horseshoe Atoll, which accumulated in the Midland basin during late Paleozoic time. The structure is a limestone reef ranging in thickness from about 100 ft on the flanks to about 750 ft on the crest, with an aver-age of about 213 ft. The average producing depth is 6,700 ft. Initial pressure was 3,122 producing depth is 6,700 ft. Initial pressure was 3,122 psig at -- 4,300 ft subsea. Initial temperature was 132 degrees F. psig at -- 4,300 ft subsea. Initial temperature was 132 degrees F. The porosity is primarily intercrystalline and effectively ranges from about 2.5 to 14 percent. Effective permeability ranges from about 0.1 to 51. 0 md. permeability ranges from about 0.1 to 51. 0 md.The reservoir was discovered in Nov. 1948 when Chevron Oil Co. completed its Jessie Brown No. 2-1 well at a depth interval of 6,334 to 6,414 ft for an initial flow of 22 BOPD of 43.5 degrees API oil. This discovery was named the Kelly-Snyder field. Soon afterward, other operators discovered the Diamond "M" and Sharon Ridge Canyon fields to the south. Development drilling revealed that the three fields merged to form one continuous reservoir. Subsequent development was rapid and essentially complete by Nov. 1951, when 1.617 producing wells had been drilled by 88 different operators. There was also extensive Canyon Reef development to the north of Kelly-Snyder in the Cogdell field, but early performance indicated that it was not connected. The reservoir pressure declined by 50 percent after producing only 5 percent of the oil. This indicated that producing only 5 percent of the oil. This indicated that solution gas dove was the primary producing mechanism. It was apparent from the rapid pressure decline that a pressure-maintenance program would be required to prevent excessive loss of reserves. It was estimated that only 19 percent of the original oil in place could be recovered by primary depletion. Unitization agreements in the Diamond "M" and Sharon Ridge Canyon fields were approved and water injection was initiated into Diamond "M" in late 1951. As a result of reservoir studies and information derived from the Diamond "M" project, the operators and royalty owners in the Kelly-Snyder field agreed to unitize to begin pressure maintenance. In 1953, the Texas Railroad Commission approved formation of the SACROC (Scurry Area Canyon Reef Operators Committee) Unit, which encompasses about 98 percent of the Kelly-Snyder field. SACROC contains 49,895 acres. (There were 1,258 wells as of Jan. 1973.) The unit was first operated in three segments by Standard Oil of Texas (now a part of Chevron Oil Co.), Sun Oil Co., and Mobil Oil Corp. under a joint unit-manager's office. Chevron was elected operator for the entire SACROC Unit in May 1962. Water injection in SACROC began in Sept. 1954 into 53 wells located along the longitudinal axis of the crest of the reef. This unique pattern is often referred to as the "center-line" waterflood at SACROC. To minimize migration, the SACROC operators established an injection-row "fence" of wells along the boundaries of Diamond "M." JPT P. 1241

Effect of Supercritical Carbon Dioxide (CO2) on Construction Materials

Abstract Laboratory tests showed that properly welded X-60 pipeline steel was not susceptible to environmental failure in supercritical carbon dioxide (CO2); and corrosion rates were less than 0.02 mils penetration per year (MPY). Other tests showed penetration per year (MPY). Other tests showed nonmetallic seals to be susceptible to damage. Seals constructed from Teflon, nylon, semi-rigid polyurethanes and ethylene-propylene rubber were polyurethanes and ethylene-propylene rubber were acceptable. Thin-film coatings and centrifugally cast cement also were acceptable pipe linings. Introduction Operation of the SACROC carbon dioxide-miscible secondary recovery project involves gathering, pipelining, and injecting more than 200,000,000 pipelining, and injecting more than 200,000,000 scf/D of carbon dioxide (CO2) into selected wells at a pressure of 2,400 psia. Waste CO2 is collected at approximately ambient conditions from four natural gas stripping stations. Thirteen compressors, totaling nearly 75,000 hp, are used to compress the gas to 2,000 to 2,400 psia. The gas is transported 232 miles in a 16- and 12-in. diameter pipeline to the Kelly-Snyder field, Scurry County, pipeline to the Kelly-Snyder field, Scurry County, Tex., where an additional 6,500 hp is used further to compress and to inject the gas at 2400 psia. Composition of the waste CO2 varies at each of the four stripping stations. The gas may contain 3 to 15 percent light hydrocarbons (chiefly methane), with up to 300 ppm hydrogen sulfide and a water content up to saturation. According to pipeline specifications, the mixed high-pressure gas contains at least 90 mol percent CO2 with the balance consisting of C1-C6 hydrocarbons. The mixed gas also contains less than 50 ppm water vapor and less dean 300 ppm hydrogen sulfide. In service, the line temperature varies from 45 to 120 degrees F. Before construction, it was necessary to know how supercritical CO2 would affect welded X-60 pipeline steel and other materials that might be used pipeline steel and other materials that might be used in the system. Laboratory tests were made after a literature search failed to produce the needed information. APPARATUS The apparatus used to simulate SACROC CO2 pipeline conditions is shown in Fig. 1, which shows pipeline conditions is shown in Fig. 1, which shows that the CO2 charging system consists of a source of CO2, a molecular sieve desiccator, a Sprague compressor unit, and an accumulator. Compressed CO2 is stored in the accumulator at 3,500 psig and nitrogen is used to maintain the pressure. When needed, hydrocarbon gas also can be supplied separately to the accumulator. Compressed CO2 at 2,000 psig is supplied from the accumulator to each of the three test cells via a regulator and check valves, V-37 and V-38. Test Cell 1 has a separate pump to circulate the CO2. Test Cells 2 and 3 are connected in series with a second circulating pump. Pump velocities can be varied but usually are set to develop a lineal flow rate of 30 to 40 in./min in the test cells. Test Cells 1 and 2 are equipped with Panametrics hygrometer probes to monitor the water content. probes to monitor the water content. The test cells also have connections to inject H2S and water and to sample the gas composition. Hydrogen sulfide content is monitored with Kitagawa detector tubes (0.01 to 0.17 volume percent). Test temperature is maintained at 72 2 degrees F. Heating mantles (not shown) can be attached to the cells to maintain a temperature of 130 degrees 2 degrees F when needed. WELDED X-60 PIPELINE STEEL TESTS The purpose of these tests was to determine the effect of simulated SACROC CO2 pipeline conditions on field-welded X-60 steel. Six manufacturers were contacted and from each were obtained samples of pipe that were at least 12 in. in diameter and with pipe that were at least 12 in. in diameter and with a minimum wall thickness of 0.344 in. Compositions of the pipe samples appear in Table 1. SPEJ P. 227

Evaluation and Design of a CO2 Miscible Flood Project-SACROC Unit, Kelly-Snyder Field

Investigations of alternative methods for improving recovery in the SACROC Unit showed that an inverted nine-spot miscible flood program consisting of injecting CO, driven by water would be the most effective and economical. Under such a scheme, the predicted ultimate recovery would be some 230 million barrels more than is expected from the original water injection program. program. Introduction The Kelly-Snyder field, discovered in 1948, is one of the major oil reservoirs in the U. S., having approximately 2 3/4 billion bbl of oil originally in place. The early performance history of the field indicated that the primary production mechanism was solely solution gas drive, which would probably result in an ultimate recovery of less than 20 percent of the original oil in place. The SACROC Unit was formed in 1953, and in Sept. 1954 a massive pressure maintenance program was started. Water was injected into a center-line row of wells along the longitudinal axis of the reservoir. This program, together with controlled production under unitized operations, has effectively rebuilt bottom-hole pressure, restored a large portion of the reservoir to liquid-saturated conditions, and stabilized producing GOR's at near solution levels. producing GOR's at near solution levels. Although the performance of the water injection program was very encouraging, technical program was very encouraging, technical representatives of the major Unit owners were constantly investigating potential methods of improving the ultimate oil recovery over that expected from the water injection program. In 1968, a technical committee, investigating potential alternatives, recommended that a water-driven potential alternatives, recommended that a water-driven slug of carbon dioxide be used to miscibly displace the oil in the non-water-invaded portion of the reservoir and that a pattern injection program be developed in this area to implement the slug process and improve ultimate oil recovery. This paper presents a summary of the methods used in evaluating alternatives and designing the final program of CO2 injection, which was begun in early 1972. Reservoir The Kelly-Snyder field, in Scurry County (West Texas) is the major unitized field among four contiguous fields along the 35- X 5-mile Canyon Reef formation. The formation is a Pennsylvanian age limestone occurring at an average depth of 6,700 ft and is a northeast-southwest trending massive reef buildup with thinner, gently sloping flanks. Formation thickness varies from an average of 800 ft on the crest of the structure to less than 50 ft on the flanks, and averages 213 ft over all. The SACROC Unit constitutes about 98 percent of the Kelly-Snyder field and includes 1,256 wells and just under 50,000 acres. The unitized reservoir is generally bounded on the east and west by porosity development and on the northeast and southwest by offsetting units. An oil/water contact, although poorly defined in some areas, occurs throughout most of the Unit area. Only very limited water influx was detected during pressure depletion, indicating a relatively small aquifer in the immediate area. A summary of basic reservoir data is given in Table 1. Reservoir oil was initially undersaturated at an original BHP of 3,122 psig, and had a solution gas content of slightly under 1,000 scf/STB and a bubblepoint pressure of 1,805 psig. P. 1309

A new Genus and Species of Shrew from the Upper Pliocene of Texas

A new genus and species of shrew is described from the upper Pliocene Beck Ranch local fauna of Scurry County, Texas. Among fossil and living American shrews, the new shrew most closely resembles the extinct Notiosorex jacksoni Hibbard.

Reinjection of Large Volumes of Produced Water in Secondary Operations

Abstract A study was made of the operating performance histories of a pressure-maintenance and four waterflood projects in the Permian Basin area, where large volumes of produced water have been reinjected into the producing formations. The projects reviewed include a wide range of characteristics: open and closed water systems, volumes of reinjected water froth 2,200 to 12,500 B/D, sand and limestone formations, depths of 1.300 to 6,750 ft. average permeabilities from 17 to 275 md, bare and protected facilities, and 10- to 50-year project life. Each project exhibited performance data which indicated that reinjection of large volumes of produced water provides a good source of injection fluid, results in practical and prudent salt water disposal and, in many cases, results in conservation of fresh water for future domestic needs. Introduction The increasing difficulty of finding adequate new oil reserves has caused almost every field in West Texas to be reviewed for possible secondary recovery applications. Because most secondary recovery processes use water, the availability and prudent utilization of water are very important to all oil operators. Standard Oil Co. of Texas' production operations in West Texas include numerous water floods, and several of these projects are reviewed and discussed in this paper. The case histories presented cover handling and reinjecting large volumes of produced water. The fields presented, as shown in Fig. 1. include SACROC unit, Howard-Glasscock, North Ward-Estes. Keystone-Colby sand, and South Ward. The combined cumulative primary and waterflood recovery of these fields to Jan., 1965. is 878.8 million bbl. Pertinent reservoir and waterflood data for the Standard of Texas' projects in each field are shown in Tables 1 and 2. Equipment used and materials for construction in each injection system are shown in Table 3. Waterflood performance histories are shown in Figs. 2 through 7. Schematic flow diagrams of the injection systems are shown in Figs. 9 through 13. SACROC Unit History and Development The Canyon Reef reservoir of the Kelly-Snyder field in Scurry County was discovered in Nov., 1948. The field now encompasses some 50,000 productive acres and 1,321 wells. Cumulative field recovery to Jan., 1965, is 322.4 million bbl. The reef, a limestone formation, is a low mound-type structure varying In thickness from 0 to 800 ft. The field was essentially developed by 1951; and, after extensive negotiations, the field was unitized with a unit manager and three segments, each operated by a working-interest owner effective March, 1953. Standard of Texas was designated unit operator on May 1, 1962. JPT P. 781ˆ

Consolidation and LACT in the SACROC Unit

Abstract Installation of full-scale consolidation and lease automatic-custody-transfer oil delivery stations was commenced in the SACROC unit during 1957. By Feb., 1963, all the 42,000 BOPD production was being delivered through 12 LACT units. Equipment used in the LACT installations is of varied manufacture and design. Oil deliveries through the LACT units range from approximately 1,000 BID at the smallest station to 12,000 BID at the largest. Both dump-tank meters and positive displacement meters are used. History of the development of the SACROC unit consolidation and LACT program and the operating experience for the various types of installations are presented. Introduction The Kelly-Snyder field, Scurry County, Tex., was discovered in Nov., 1948. The producing formation, the Canyon Reef limestone, lies at a depth of about 6,600 to 6,900 ft. Development of the field proceeded at a rapid pace until it was essentially completed by the end of 1953. The field now contains 1,316 wells overlying approximately 52,000 oil-productive acres. In Dec., 1950, the Scurry Area Canyon Reef Operators Committee was formed, this name later being abbreviated to SACROC, and unitization studies were begun in Jan., 1951. Unitization of the major portion of the field became a reality on March 1, 1953, when SACROC unit began operation. The unit now contains 1,256 wells and approximately 50,000 productive acres, which overlie about 99 per cent of the productive formation of the Kelly-Snyder field. Initially, the operation of SACROC was under the supervision of a Unit Manager's Office, and the field was divided into three segments, each operated by one of the working interest owners-Standard Oil Co. of Texas, Mobil Oil Co. and Sun Oil Co. On May 1, 1962, after amendment and ratification of the Unit Operating Agreement, Standard Oil Co. of Texas became the unit operator. At the time SACROC became effective in 1953, there were approximately 400 active tank batteries within the area of the Kelly-Snyder field operated by the unit. Unitization made it possible to consider extensive tank-battery consolidation. By 1957 pressure-maintenance operations had resulted in stabilized producing conditions. Facilities had been installed to collect and return all produced water to the Canyon reef reservoir. Some consolidation work on a small scale had been done in the unit prior to 1957 as it became desirable to combine manifolds because of water line extensions and other field operating conditions. During the latter part of 1957 a full-scale program of consolidation of producing facilities and installation of automatic custody transfer equipment was commenced in SACROC unit. By Feb., 1963, all the 42,000 BOPD production from unit wells was collected into 12 central batteries and was being delivered to five pipeline companies through automatic-custody-transfer units. Experience in the unit has shown that it is economically feasible to replace conventional producing facilities with automatic-custody-transfer equipment in a developed field. In addition to improving operating efficiency, the centralization of producing facilities into large central batteries has made it economically feasible to collect and sell tank vapors which previously would have been vented to the atmosphere. Delivery of oil through LACT units has virtually eliminated breathing and filling losses which occurred in normal storage of oil in stock tanks without vapor control. As a result of the LACT installations, the amount of oil stored, closing stock, above ground in the unit has been reduced from approximately 160,000 bbl in March, 1957, to approximately 47,000 bbl since March, 1963.Representatives of a number of the working interest owners in SACROC contributed to the planning of the consolidation and LACT program. Early work and planning were done at a time when automatic custody transfer of oil was in the early stages of development. The five pipeline companies which gather unit oil have furnished assistance and have been very cooperative throughout the development of the consolidation and LACT work. Both dump-tank type units and PD meters have been installed and operated. LACT units are now operated which handle approximately 1,000 BOPD at the smallest station to 12,000 BOPD at the largest. The purpose of this paper is to discuss the development of the consolidation and LACT program in the unit, to describe the equipment used, and to discuss the results obtained from the program. JPT P. 751ˆ