South Belridge Field Research Articles

Case History of Reservoir Subsidence and Wellbore Damage Management in the South Belridge Diatomite Field

Summary Production of fluids from the shallow, thick, and low-strength Diatomite reservoir in the South Belridge Field has resulted in reservoir compaction, surface subsidence, and numerous well failures. The most severe subsidence problems occurred while the field was under primary recovery, prior to implementation of waterfloods for pressure support. Consequently, a significant number of wells in the field have incurred casing damage, which proportionately limits the utility of these wellbores for continued production and routine wellwork operations. The nature of casing damage varies significantly depending on the location in the field, however casing shear ("kinks") generally produces the most severe problems in retaining full wellbore utility since it limits tool passage (e.g., packers, scrapers, etc. ) and is not economical to repair using conventional milling tools. Since the mid-1980s, surveillance has been in place to monitor and assess the magnitude and progression of surface subsidence, reservoir compaction, and wellbore damage in Exxon's operations of Section 19 in the South Belridge Field. The surveillance includes the use of ground elevation markers and a variety of production logs—several of which involve novel application and log interpretation. These data subsequently were used to develop and verify hybrid geomechanics and wellbore geometric models for assessing casing damage, identifying well operability and wellbore utility limits, and forecasting the remaining wellbore life from which a reservoir management plan and wellbore management operational strategies were established. A key ingredient in the implementation of this plan and operational strategies involved a cooperative tool development with a major oil tool service company to repair casing kinked wellbores as an alternative to re-drilling wells. In this article we provide a case history that describes the various synergistic reservoir and wellbore management activities designed to effectively mitigate subsidence-induced operational problems and the accompanying field benefits resulting from their implementation.

Steam Injection Project in Heavy-Oil Diatomite

Summary A steam injection project was conducted in diatomite containing heavy, biodegraded oil (12°API, ∼3,000 cp) in the South Belridge field, Kern County, California. The diatomite interval tested (the San Joaquin, Etchegoin, and Belridge diatomites) underlies an active steamflood in the sandstone of the Tulare formation. Initially, the test was to determine the viability of cyclic steam recovery from an unpropped, steam fractured completion in the diatomite. Four standard steam cycles were completed, with sluggish oil recovery [oil–steam ratios (OSR) were less than 0.1]. The well was then hydraulically fractured and propped. Two additional steam cycles were completed that had considerably greater oil recovery (OSR>0.2). The project was then configured for steamdrive by drilling a closely spaced producer. The new producer was initially completed with a propped hydraulic fracture and cycled once. The original cyclic producer was converted to continuous injection, and a two-well steamflood was operated for more than 1 year. During the steamflood, heavy oil was mobilized and response has been continuous. The configuration of the "pattern," with only one producer, results in poor capture efficiency. The performance of this incomplete pattern has been, as expected, poor (<0.1 OSR), but steam injection is shown to be a promising recovery technique for the heavy oil diatomite. The process is applicable to California diatomites, or any other high porosity, low permeability, shallow reservoirs that contain a significant concentration of heavy oil.

Use of 3D Reservoir Characterization to Plan and Implement Horizontal Heavy Oil Development of the Tulare Reservoir South Belridge Field, California

Use of 3D Reservoir Characterization to Plan and Implement Horizontal Heavy Oil Development of the Tulare Reservoir South Belridge Field, California

Field-Scale and Wellbore Modeling of Compaction-Induced Casing Failures

Summary Presented in this paper are the results and verification of field- and wellbore-scale large deformation, elasto-plastic, geomechanical finite element models of reservoir compaction and associated casing damage. The models were developed as part of a multidisciplinary team project to reduce the number of costly well failures in the diatomite reservoir of the South Belridge Field near Bakers-field, California. Reservoir compaction of high porosity diatomite rock induces localized shearing deformations on horizontal weak-rock layers and geologic unconformities. The localized shearing deformations result in casing damage or failure. Two-dimensional, field-scale finite element models were used to develop relationships between field operations, surface subsidence, and shear-induced casing damage. Pore pressures were computed for eighteen years of simulated production and water injection, using a three-dimensional reservoir simulator. The pore pressures were input to the two-dimensional geomechanical field-scale model. Frictional contact surfaces were used to model localized shear deformations. To capture the complex casing-cement-rock interaction that governs casing damage and failure, three-dimensional models of a wellbore were constructed, including a frictional sliding surface to model localized shear deformation. Calculations were compared to field data for verification of the models.

Abstract: 3D Seismic Imaging of the Shallow Tulare Sandstone at South Belridge Field, CA - Results and Impact on Reservoir Development

Abstract: 3D Seismic Imaging of the Shallow Tulare Sandstone at South Belridge Field, CA - Results and Impact on Reservoir Development

Mapping Steam and Water Flow in Petroleum Reservoirs

Summary During the past 5 years, we have applied high-resolution geophysical methods [crosswell seismic and electromagnetics (EM) and passive seismic] to map and characterize petroleum reservoirs in the San Joaquin Valley and to monitor changes during secondary-recovery operations. The two techniques provide complementary information. Seismic data reveal the reservoir structure, whereas EM measurements are more sensitive to the pore-fluid distribution. Seismic surveys at the South Belridge field were used to map fracture generation and monitor formation changes caused by the onset of steamflooding. Early results show possible sensitivity to changes in gas saturation caused by the steamflooding. Crosswell EM surveys were applied at a shallow pilot at Lost Hills for reservoir characterization and steamflood monitoring. Images made from baseline data clearly show the distribution of the target oil sands; repeated surveys during the steamflood allowed us to identify the boundaries of the steam chest and to predict breakthrough accurately. Applications of the EM techniques in steel-cased wells are at an early stage, but preliminary results at Lost Hills show sensitivity to formation resistivity in a waterflood pilot.

Integrated Reservoir Characterization of a Tulare Steamflood Finds Bypassed Oil - South Belridge Field, Kern County, California: ABSTRACT

Reservoir quality and producibility are directly related to the characteristics of the depositional lithofacies. Electric log gamma ray/resistivity profiles were used to define facies trends within the Tulare steamflood at South Belridge. Channel and non-channel facies profiles are distinctive across the lease with the channel sands having the better quality reservoir and greater net pay values. Sidewall core permeabilities were averaged over the main producing Tulare intervals with the channels averaging 2000-3000 millidarcies and non-channels 200-500 millidarcies. This supports the lithofacies trend and net pay maps. Although the approach is qualitative, it illustrates the dramatic permeability contrast between the channel and non-channel lithofacies. Temperature maps using downhole temperature surveys and flowline temperatures indicate channel facies temperatures up to 300[degrees] with the non-channel facies having 90[degrees] to 100[degrees] temperatures (near ambient). Higher temperatures also relate to higher average daily production rates for channel associated wells. Channel wells averaged greater than 30 BOPD while non-channel wells averaged 10 BOPD or less. New and replacement well nations have been high graded resulting in favorable production responses. Integration of the lithofacies, permeability and temperature data plus ongoing preventive production optimization work has led to a more efficient Tulare steamflood and identification of bypassed oilmore » on the King-Ellis lease in the South Belridge Field.« less

South Belridge Tulare Simulation Study: Steamflood in a Heterogeneous Stratified Reservoir

Summary Thermal reservoir simulation is used to develop an operational strategy for the Tulare sand of the South Belridge field. History matching of an ongoing steamflood that has been in operation since 1981 is used to test the validity of the model. The primary purpose of the simulation study is to evaluate and design the optimum steamflood for an expansion project in the undeveloped, southern portion of the field. The simulation model also is used to study operating policy options for current operations as well as for new development. This study results in the recommendation that a 5-acre, nine-spot pattern be developed for the Southern Expansion Project. Study of operating policy shows that steamflood performance can be improved by shutting in marginal producing layers and optionally cutting back the steam-injection rate.

Well kill (quenching) study of thermal producers in the South Belridge field, California : J. W. Fram, SPE Production & Facilities, 9(3), 1994, pp 165–170

Well kill (quenching) study of thermal producers in the South Belridge field, California : J. W. Fram, SPE Production & Facilities, 9(3), 1994, pp 165–170

Oil Gravity Distribution in the Diatomite at South Belridge Field, Kern County, CA: Implications for Oil Sourcing and Migration: ABSTRACT

Understanding oil gravity distribution in the Belridge Diatomite has led to economic infill development and specific enhanced recovery methods for targeted oil properties. To date more than 100 wells have provided samples used to determining vertical and areal distribution of oil gravity in the field. Detailed geochemical analyses were also conducted on many of the oil samples to establish different oil types, relative maturities, and to identify transformed oils. The geochemical analysis also helped identify source rock expulsion temperatures and depositional environments. The data suggests that the Belridge diatomite has been charged by a single hydrocarbon source rock type and was generated over a relatively wide range of temperatures. Map and statistical data support two distinct oil segregation processes occurring post expulsion. Normal gravity segregation within depositional cycles of diatomite have caused lightest oils to migrate to the crests of individual cycle structures. Some data suggests a loss of the light end oils in the uppermost cycles to the Tulare Formation above, or through early biodegradation. Structural rotation post early oil expulsion has also left older, heavier oils concentrated on the east flank of the structure. With the addition of other samples from the south central San Joaquin area, wemore » have been able to tie the Belridge diatomite hydrocarbon charge into a regional framework. We have also enhanced our ability to predict oil gravity and well primary recovery by unraveling some key components of the diatomite oil source and migration history.« less

Well Kill (Quenching) Study of Thermal Producers in the South Belridge Field, California

Summary This paper presents a field study confirming that damage occurs during kill (quenching) operations of thermal producers in the South Belridge field, Kern County, CA. Implementation of the recommendations from this study are expected to decrease damage that occurs during quenching by an average of 0.5 BOPD/kill. Results indicate that producers completed with openhole, gravel-packed, slotted liners in high-permeability sandstones can sustain substantial, irreversible damage when subjected to unfiltered produced-water kills. The damage results when previously produced sand and fines, which have settled in the flowline, are reinjected into the wellbore. Most of the damage is in the slots and gravel pack. Previous studies, field tests, and laboratory work quantifying the amount and site of the damage are detailed. Methods of determining water-quality specifications needed to minimize damage that occurs during well kills are outlined. The approach presented can be used to identify and quantify damage in any field where producers require kills before workover operations. The current recommended kill procedure is also included.

Geological Aspects of Drilling Horizontal Wells in Steam Flood Reservoirs, West Side, Southern San Joaquin Valley, California: ABSTRACT

Shell Western E P Inc. has drilled 11 horizontal wells in four mature steam floods in the Coalinga, South Belridge, and Midway-Sunset fields. Two medium radius wells are producing from the Pliocene Etchegoin Formation in Coalinga. One medium radius well is producing from the Pleistocene Tulare Formation in South Belridge field. Three short radius and five medium radius wells are producing from the upper Miocene, Sub-Hoyt and Potter sands in Midway-Sunset field. Horizontal wells at the base of these reservoirs and/or structurally downdip near the oil-water contact are ideally suited to take advantage of the gravity drainage production mechanism. Reservoir studies and production experience have shown these horizontal wells should increase reserves, improve recovery efficiency, improve the oil-steam ratio, and improve project profitability. Geological considerations of targeting the wells vary between fields because of the different depositional environments and resulting reservoir characteristics. The thin sands and semicontinuous shales in the Tulare Formation and the Etchegoin Formation require strict structural control on the top and base of the target sand. In the Sub-Hoyt and Potter sands, irregularities of the oil-water contact and sand and shale discontinuities must be understood. Logging and measurement while drilling provide geosteering capability in medium radius wells.more » Teamwork between all engineering disciplines and drilling and producing operations has been critical to horizontal well success.« less

Tulare Formation Permeability and Fluid Variations, South Belridge Field, Kern County, California

Tulare Formation Permeability and Fluid Variations, South Belridge Field, Kern County, California

Chromatography Helps Optimize Development of Diatomite in the South Belridge Field, Kern County, California

Chromatography Helps Optimize Development of Diatomite in the South Belridge Field, Kern County, California

Use of Pulsed-Neutron Capture Logs To Identiffy Steam Breakthrough

Summary Identification of steam-breakthrough zones in a stacked sand/shale sequence with variable lateral continuity is difficult. Such identification, however, would allow the modification of field operations to enhance recovery through improved vertical sweep and heat injection. Twenty pulsed-neutron capture (PNC) logs were run to identify the steam-breakthrough zone(s) in a seven-pattern area of Mobil's Middle Expansion (MIDX) Steamflood Project in the South Belridge field. These PNC data were combined with data from recent replacement wells and a detailed geologic analysis. Evaluation of this combined information allowed identification of potential steam-breakthrough zone(s), and operations were modified to reduce and eliminate steam breakthrough.

South Belridge Field, Borderland Basin, U.S., San Joaquin Valley

South Belridge is a giant field in the west San Joaquin Valley, Kern County. Cumulative field production is approximately 700 MMBO and 220 BCFG, with remaining recoverable reserves of approximately 500 MMBO. The daily production is nearly 180 MBO from over 6100 active wells. The focus of current field development and production is the shallow Tulare reservoir. Additional probable diatomite reserves have been conservatively estimated at 550 MMBO and 550 BCFG. South Belridge field has two principal reservoir horizons; the Mio-Pliocene Belridge diatomite of the upper Monterey Formation, and the overlying Plio-Pleistocene Tulare Formation. The field lies on the crest of a large southeast-plunging anticline, sub-parallel to the nearby San Andreas fault system. The reservoir trap in both the Tulare and diatomite reservoir horizons is a combination of structure, stratigraphic factors, and tar seals; the presumed source for the oil is the deeper Monterey Formation. The diatomite reservoir produces light oil (20-32{degree} API gravity) form deep-marine diatomite and diatomaceous shales with extremely high porosity (average 60%) and low permeability (average 1 md). In contrast, the shallow ({lt}1000 ft (305 m) deep) overlying Tulare reservoir produces heavy oil (13-14{degree} API gravity) from unconsolidated, arkosic, fluviodeltaic sands of high porosity (average 35%)more » and permeability (average 3000 md). The depositional model is that of a generally prograding fluviodeltaic system sourced in the nearby basin-margin highlands. More than 6000 closely spaced, shallow wells are the key to steamflood production from hundreds of layered and laterally discontinuous reservoir sands which create laterally and vertically discontinuous reservoir flow units.« less

Steamflooding in a Waterdrive Reservoirs Upper Tulare Sands, South Belridge Field

Summary A steamflood project in the strong edgewater-drive Upper Tulare reservoir at South Belridge recovered about 31% of the original oil in place (OOIP) at a cumulative steam/oil ratio (SOR) of 2.7 vol/vol. Seven years of downdip steam injection depressed water influx and created an oil bank updip from the injectors. Response continued under the influence of returning aquifer water and heat scavenging after the injectors were shut down. Numerical reservoir simulation of the historical steamflood performance indicated that the high production/injection capacity (P/I) ratio induced early water encroachment and partial quenching of the growing steam zone. Restarting downdip steam injection at much higher rates after 6 years without injection was shown to recover more oil than continuing the steamflood with either a seven-spot or inverted nine-spot pattern. An efficient steamflood operating policy in an edgewater-drive environment involves overproducing in the oil column to reduce reservoir pressure combined with high-rate downdip pumping of the aquifer to reduce water inflow during steam injection. Downdip steam injection rates greater than 100 B/D-acre and P/I ratios of about 1.4 STB/STB emerged as reasonable operating parameters in several projects.

Mixing of Biogenic Siliceous and Terrigenous Clastic Sediments: South Belridge Field and Beta Field, California: ABSTRACT

The intermixing and interbedding of biogenically derived siliceous sediment with terrigenous clastic sediment in reservoirs of upper Miocene age provides both reservoir rock and seal and influences productivity by affecting porosity and permeability. Miocene reservoirs commonly contain either biogenic-dominated cyclic diatomite, porcelanite, or chert (classic Monterey Formation) or clastic-dominated submarine fan sequences with interbedded or intermixed siliceous members of biogenic origin. Biogenic-clastic cycles, 30-180 ft thick, at South Belridge field were formed by episodic influx of clastic sediment from distant submarine fans mixing with slowly accumulating diatomaceous ooze. The cycles consist of basal silt and pelletized massive diatomaceous mudstone, overlain by burrowed, faintly bedded clayey diatomite and topped by laminated diatomite. Cycle tops have higher porosity and permeability, lower grain density, and higher oil saturation than clay and silt-rich portions of the cycles. Submarine fan sediments forming reservoirs at the Beta field are comprised of interbedded sands and silts deposited in a channelized middle fan to outer fan setting. Individual turbidites display fining-upward sequences, with oil-bearing sands capped by wet micaceous silts. Average sands are moderately to poorly sorted, fine- to medium-grained arkosic arenites. Sands contain pore-filling carbonate and porcelaneous cements. Porcelaneous cement consists of a mixture of opal-A, opal-CT,more » and chert with montmorillonite and minor zeolite. This cement is an authigenic material precipitated in intergranular pore space. The origin of the opal is biogenic, with recrystallization of diatom frustules (opal-A) into opal-CT lepispheres and quartz crystals. Porcelaneous cement comprises 4-21% of the bulk volume of the rock. Seventy percent of the bulk volume of the cement is micropore space.« less

Reservoir Compaction of the Belridge Diatomite and Surface Subsidence, South Belridge Field, Kern County, California: ABSTRACT

Abstract Surface subsidence due to reservoir compaction during production has been observed in many large oil fields. Subsidence is most obvious in coastal and offshore fields where inundation by the sea occurs. Well known examples are Wilmington field in California and Ekofisk field in the North Sea. In South Belridge field the Belridge diatomite member of the late Miocene Reef Ridge Shale has proven prone to compaction during production. The reservoir, a high porosity, low permeability, highly compressive rock composed largely of diatomite and mudstone, is about 1000 ft thick and lies at an average depth of 1600 ft. Reservoir compaction within the Belridge diatomite due to withdrawals of oil and water in section 12, T28S, R20E, MDBM the estimated peak subsidence rate reached -7.50 ft/yr in July 1985, after 1 yrs of production from the Belridge diatomite reservoir. Since production from the Belridge diatomite reservoir commenced in February, 1984, the surface of the 160 acres producing area has subsided about 12.50 ft. This equates to an estimated reservoir compaction of 30 ft in the Belridge diatomite and an average loss of reservoir porosity of 2.4% from 55.2% to 52.8%. Injection of water for reservoir pressure maintenance in the Belridge diatomite began in June, 1987, and has been effective in mitigating subsidence and repressurizing the reservoir to near-initial pressure. An added benefit of water injection has been improved recovery of oil from the Belridge diatomite by waterflood. The operation of four other water injection projects in South Belridge Field in the Belridge diatomite reservoir suggests that reservoir compaction and surface subsidence is a common occurrence in the field.

Rationale For Low Injection Rates And Pressure Cycles For Firefloods In Heavy Oil Reservoirs

Abstract A reservoir flow path model with low injection rates has been used to develop an alternate approach to fire floods in heavy oil reservoirs with initial oil mobility. Low injection rates are used to maintain and propagate the firefront in the reservoir. The pressures in the burn volume and the/low path are maintained lower than that in the unaffected reservoir, allowing oil from the unaffected reservoir to drain into the flow path and to increase production. The fireflood process also generates upgraded oil with lower viscosities to further enhance oil mobility in the flow path. Pressure cycles can be used to facilitate additional oil resaturation of the flow path to alleviate severe gas channelling ahead of the burn front. Injection and producing well casing pressure histories and fluid analysis data from the Husky Tangleflags Fireflood Project are reviewed to illustrate the beneficial effects of low injection rates and pressure cycles. Introduction The in-situ fireflood recovery process is one of the thermal techniques used for enhanced recovery from heavy oil reservoirs(1) Quite often, the design of fireflood projects were based on displacement considerations(2, 3). Invariably, some non-radial distribution of the burn front had been observed(2, 4, 5). Reduced production due to increased casing pressures(5) and elevated downhole temperatures(1, 4) were experienced and were considered to be sources of major problems. A reservoir flow path model is proposed for firefloods using low injection rates in heavy oil reservoirs having some initial oil mobility. The pressures in both the burn zone and the flow path are lower than the pressure in the unaffected reservoir, allowingoil drainage into the flow path to increase production. The oil mobility is further enhanced by the reduced viscosity of the upgraded oil. Pressure cycles can be used to transport additional oil from the unaffected reservoir into the flow path to alleviate severe gas channelling ahead of the burn front. Selected injection and producing well casing pressure histories together with fluid analysis data from the Husky Tangleflags Fireflood Project are reviewed to illustrate the beneficial effects of reservoir fluid drainage into the flow path and reduction in oil viscosities due to the fireflood upgraded oil. Classical Fireflood Design One basic design criteria for the fireflood process has been the correlation between oil recovery and burn volume. Before inalizing the design of a fireflood project, a burn tube test was run to determine the burn characteristics of that particular reservoir. From the burn tube data, oil displaced and air requirement values are determined to assist in the design and operation of the fireflood project(2). Based on the field test results from a fireflood project in the South Belridge Field and related laboratory studies, Gates and Ramey(3) provided a correlation between oil displaced and volume burned as a method for engineering fireflood projects. These design parameters are probably good starting points for most fireflood projects. For a fireflood design in a specific reservoir, an economic oil production rate is assumed and used in conjunction with these design parameters to determine the injection rate necessary for an economic fireflood project.