Open Hole Wireline Logs Research Articles

Wireline Logging Operation Uses Water-Based Drilling Fluid in HP/HT Gulf of Mexico Well

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 210021, “Wireline Logging in High-Overbalance, High-Pressure/High-Temperature Deepwater Gulf of Mexico Well With Water-Based Reservoir Drilling Fluid,” by Martin Tjioe, Jeremy McCaslin, and Jonathan J. Brege, SPE, Shell, et al. The paper has not been peer reviewed. _ Openhole wireline logging, because of its lower overpull capacity relative to logging while drilling, is subject to increased stuck-tool risk. The risk increases in higher-overbalance environments typical for depleted reservoirs, but other aspects of sticking risk can be managed. The complete paper describes the measures taken in an openhole wireline-logging operation in a deepwater Gulf of Mexico (GOM) well under nearly 7,000-psi overbalance in a high-pressure/high-temperature (HP/HT) slimhole environment using water-based reservoir drilling fluid (RDF) to achieve an efficient logging operation without incurring lost time attributed to conveyance-related issues. Introduction The wireline data-acquisition program was planned for an injector well in the deepwater GOM development field. The goal of the well was to maintain reservoir pressure through waterflooding, maximize recovery, and appraise the downdip portion of the fault block. The target was an aeolian sandstone reservoir at a depth of approximately 25,500 ft total vertical depth subsea featuring 19% porosity and permeability in the tens-of-millidarcy range. The reservoir had depletion of 6,850 psi; the well penetrated 174 ft of the reservoir with a hole size of 7 in. and a deviation of 25°. The injector used an openhole stand-alone-screen completion concept. Water-based RDF was used so that filter-cake material could be removed using a breaker fluid to enable matrix injection. Using a 13.5-lbm/gal mud weight, the wireline operation was performed under a downhole pressure of 17,900 psi (overbalance of 6,950 psi). The maximum temperature recorded during wireline was 320°F. Wireline Data-Acquisition Program The wireline program’s objectives were to acquire safely a profile of pressures and mobilities to identify depletion boundaries and to inform completion operations and acquire temperature data to infer the static formation temperature. During the planning phase, the well was classified as highly challenging, with a high risk of differential sticking based on the analog wireline jobs in the field. The well of interest penetrated the reservoir with the highest depletion encountered in the field at the time; because of its downdip location, it also had one of the higher downhole temperatures in the field. Several learnings from analog wells that are further detailed in the complete paper included the following: - Necessity of good hole cleaning - Reduction of toolstring length - Necessity of a water-based RDF with good fluid properties

Permeability extraction from multiple well logs using particle swarm optimization based factor analysis

In this paper, we present an innovative factor analysis algorithm for hydrocarbon exploration to estimate the intrinsic permeability of reservoir rocks from well logs. Unlike conventional evaluation methods that employ a single or a limited number of data types, we process simultaneously all available data to derive the first statistical factor and relate it to permeability by regression analysis. For solving the problem of factor analysis, we introduce an improved particle swarm optimization method, which searches for the global minimum of the distance between the observed and calculated data and gives a quick estimation for the factor scores. The learning factors of the intelligent computational technique such as the cognitive and social constants are specified as hyperparameters and calculated by using simulated annealing algorithm as heuristic hyperparameter estimator. Instead of the arbitrary fixation of these hyperparameters, we refine them in an iterative process to give reliable estimation both for the statistical factors and formation permeability. The estimated learning parameters are consistent with literature recommendations. We demonstrate the feasibility of the proposed well-log analysis method by a Hungarian oilfield study involving open-hole wireline logs and core data. We determine the spatial distribution of permeability both along a borehole and between more wells using the factor analysis approach, which serves as efficient and reliable multivariate statistical tool for advanced formation evaluation and reservoir modeling.

Deep Directional Electromagnetic Technique Improves Well-Drilling Efficiency

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 202265, “Leap of Faith From Conventional to EM Look-Ahead: A Game-Changing Technology To Improve Well Efficiency,” by Muhamad Yanuar Mahardi, Hendarsyah Hendarsyah, and Kharisma Endarmoyo, PT Pertamina, et al., prepared for the 2020 SPE Asia Pacific Oil and Gas Conference and Exhibition, originally scheduled to be held in Perth, Australia, 20–22 October. The paper has not been peer reviewed. The structure in the Matindok block in Central Sulawesi operated by Pertamina has proven producible gas reserves in the Minahaki formation. One of the main challenges in this area is the low resolution of seismic data, leading to a high depth uncertainty. The complete paper describes a technology developed to meet these challenges with the capability to map and detect lithology changes ahead of the bit in real time. Geological Background A first exploration well, PEP-001, was drilled in 2018. The structure has a Miocene carbonate buildup play, and the target reservoir is the M pinnacle carbonate reef. The PEP-001 well was planned to set the 9⅝-in. casing point above the top of the M formation. Offset wells did not show any clear markers in the thick shale above the M formation that could have been used for log correlation. In previously drilled offset wells, correlation was performed convention-ally by examination of cutting samples and on drilling breaks. However, when Well PEP-001 was drilled, no apparent drilling break was observed. By the time cuttings reached the surface, the bit had drilled into 20 m of the M formation. Because the casing covered most of the upper carbonate formation, openhole logging and well-testing data were not acquired to delineate the target formation optimally. The second exploration well, PEP-002, was planned with an objective of setting 9⅝-in. casing approximately 5 m above the top of M to acquire full-interval coverage of coring, openhole wireline logging, and well testing. This information was critical for optimal reservoir delineation to allow for accurate reserves calculation and future development. Conventional correlation methods have proven insufficient for casing point placement. The presence of limestone stringers in offset wells within proximity of the top of M presented an additional challenge. The stringers could have been misinterpreted as the main carbonate body, if interpretation were based solely on cutting samples. Real-Time Electromagnetic (EM) Look-Ahead Technology

Cased-Hole Solution Assesses Tight Reservoirs

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 197423, “Cased-Hole Solution With Fast Neutrons and Sonic Reflective Waves in Tight Reservoirs,” by Ulises Bustos, Schlumberger, Carelis Moya, Equion Energia, and David Rose, SPE, Schlumberger, et al., prepared for the 2019 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 11-14 November. The paper has not been peer reviewed. The complete paper presents a solution that assesses tight matrices and natural fractures at a level not previously achieved. At the tight-matrix level, advanced nuclear spectroscopy is carried out with a new pulsed-neutron device that achieves simultaneous time- and energy-domain measurements. A new resistivity- and salinity-independent methodology is presented for obtaining gas saturation by a measurement known as fast neutron cross section (FNXS), oil saturation from the total-organic-carbon log, mineral volumes solved from formation elemental concentrations from the energy domain, and porosity from the hydrogen index obtained from the spectroscopy time domain. Reservoir Challenges The reservoirs under analysis belong to the Colombian Pauto Complex field (Fig. 1). Wells drilled in the area have confirmed a staked structure architecture, in which three main thrust sheets can be differentiated: Miche, Guamalera, and Pauto Main. The present study was focused on the Mirador formation of the Pauto Complex, which can be described as a fluvial and shallow marine environment deposit system. The Mirador formation is divided into two zones by Middle Eocene unconformity and is almost totally composed of quartz grains and mainly cemented by silica and significant kaolinite content. An additional characteristic of this reservoir is the presence of natural fractures that contribute strongly to well productivity. The main production is from the Mirador formation and is characterized by highly complex heterogeneity and anisotropy because of a multidiagenetic process, the accumulated hydrocarbon of which is a gas rich in condensate with variations in composition. The reservoirs are located at average depths of approximately 17,000 ft in the eastern foothills of the Colombian Andes, a region characterized by high-tectonic-stress regimes and reservoirs intercalated with reactive shales. Those factors lead to challenging drilling conditions where the combination of oil-based-mud systems and small wellbore diameters (approximately 6 in.) at the target zones are the only way to minimize wellbore-stability problems. Data acquisition is also challenged because logging-while-drilling technologies are sometimes limited in small wellbores and openhole wireline logging is sometimes jeopardized by hostile hole conditions. Under these scenarios, the authors explored formation evaluation in cased-hole conditions with wireline-conveyed technologies for both matrix and natural-fracture systems. The described spectroscopy device is wireline-conveyed and consists of a nonradioactive/high-energy pulsed-neutron generator and a highly sensitive set of multidetectors equipped with advanced electronics for carrying out complex neutron-burst schemes for accurate gamma-ray spectral analysis. This achieves a broad mineral-spectrum analysis, highly significant for two key formation evaluation parameters, porosity and saturation. The porosity typically is derived from neutron measurements incorporated in the same tool, where the matrix components over the interest zones provided by this spectroscopy device ensure an accurate porosity computation. The technology provides gas saturation from a hydrogen-index-independent gas-detection device and the liquids/hydrocarbon fraction from the carbon measurement; other rock elements containing carbon also are considered for a precise saturation computation.

FEASIBILITY OF TEMPERATURE LOGGING TO FINDING HYDROCARBON-SATURATED RESERVOIRS IN CASED WELLS

Finding of hydrocarbon-saturated intervals in the wells of the old fund is one of the most promising methods for re-exploration of depleted fields. Lack of the open hole wireline logs for the wells of the old fund, forces to estimate saturation of promising intervals through casing by specialized wireline methods. Implementation of these methods associ-ated with high cost of logging, complexity, and average results. In this paper, we have studied the feasibility of the temperature logging as a relatively inexpensive early testing tool, which allows us to identify hydrocarbon-saturated inter-vals in a large number of cased wells with acceptable accuracy. Summarized theoretical information about the nature of the Earth's temperature field distribution around the well presented. Impact of saturating fluids on the final value of the thermal conductivity of a porous rock has been reviewed and one of the empirical models has been outlined. Algorithm for characterizing type of saturation by the temperature log-ging in the cased hole proposed. From the results of testing, it was concluded that promising method is consistent and viable. The success rate of the proposed method is about 50 - 60 %, which is comparable with the results of other methods for saturation estimation through casing. However, at this stage of development, the method is much of qualitative than quantitative, due to application of empirical thermal conductivity models and the lack of an acceptable solu-tion for more general theoretical models. Nevertheless, the obtained results allows us to say that the temperature logging is a relatively cheap early testing tool that allows to cover significant intervals of depths and a large number of wells with an acceptable accuracy.

Quantification of Organic richness through wireline logs: a case study of Roseneath shale formation, Cooper basin, Australia

The late Carboniferous-Middle Triassic, intracratonic Cooper basin in northeastern South Australia and southwestern Queensland is Australia's foremost onshore hydrocarbon producing region. The basin compromises Permian carbonaceous shale like lacustrine Roseneath and Murteree shale formation which is acting as source and reservoir rock.The source rock can be distinguished from non-source intervals by lower density, higher transit time, higher gamma ray values, higher porosity and resistivity with increasing organic content. In current dissertation we have attempted to compare the different empirical approaches based on density relation and Δ LogR method through three overlays of sonic/resistivity, neutron/resistivity and density/resistivity to quantify Total organic content (TOC) of Permian lacustrine Roseneath shale formation using open hole wireline log data (DEN, GR, CNL, LLD) of Encounter 1 well. The TOC calculated from fourteen density relations at depth interval between 3174.5–3369 meters is averaged 0.56% while TOC from sonic/resistivity, neutron/resistivity and density/resistivity yielded an average value of 3.84%, 3.68%, 4.40%. The TOC from average of three overlay method is yielded to 3.98%.According to geochemical report in PIRSA the Roseneath shale formation has TOC from 1 – 5 wt %.There is unpromising correlations observed for calculated TOC from fourteen density relations and measured TOC on samples. The TOC from average value of three overlays using Δ LogR method showed good correlation with measured TOC on samples.

USE OF WELL-LOGS FOR PETROPHYSICAL EVALUATION OF ABU MADI RESERVOIR IN ABU MADI - EL-QARA - NIDOCO AREA, NORTHERN NILE DELTA, EGYPT

The objective of the present study is to evaluate the reservoir characteristics of the Late Miocene Abu Madi Formation (Abu Madi Levels II and III) at Abu Madi-El-Qara-Nidoco area, northern Nile Delta, Egypt. The study area is located between Longitude 31° 13` 48`` -31° 24` 36``E and Latitude 31° 21` 36``- 31° 37` 12`` N. Open-hole wireline log data of seven wells are used in this study. The petrophysical characteristics of the studied formation are thoroughly investigated to elucidate its hydrocarbon potentialities. The vertical variation of the petrophysical characteristics is presented as Lithosaturation cross-plots. The parameters distribution maps (shale volume, porosity, fluid saturation, net pay thickness and hydrocarbon saturation) are constructed to represent the lateral variation of petrophysical characteristics. The shale model shows that the dominant shale is mainly of dispersed and laminated types. The constructed neutron-bulk density, neutron-sonic and M-N crossplots display that the main reservoir lithology is sandstone intercalated mainly with dispersed shale and minor laminated shale in Level III and dispersed to laminated shale in Level II. It is also shown that Abu Madi Formation has poor to very good porosities range from 0.03 to 0.22 for Level II and from 0.06 to 0.19 for Level III. The most favorable places for hydrocarbon reservoirs occupy southwestern part for Abu Madi Level II reservoir and in the middle, the middle-west, the middle-east and the southeastern parts for Abu Madi Level III reservoir.

Use of Well Logs for Petrophysical Evaluation of Abu Madi Reservoir in Abu Madi-ElQara-Nidoco Area, Northern Nile Delta, Egypt

The open-hole wire line log data of seven wells are used to study the petrophysical characteristics of the Late Miocene Abu Madi Formation (levels II and III) in Abu Madi-El-Qara-Nidoco area, northern Nile Delta, Egypt. The vertical variation of the petrophysical characteristics is presented as lithosaturation cross-plots. The parameters distribution maps (shale volume, effective porosity, fluid saturation, net pay thickness and hydrocarbon saturation) are used to represent the lateral variation of petrophysical characteristics. Cross plots show that the main reservoir lithology is shaly sandstone with laminated to dispersed shale in level II and dispersed shale and minor laminated shale in level III. The shale volume ranges from 0.19 to 0.71 for level II and from 0.19 to 0.47 for level III. The effective porosity ranges from 0.03 to 0.22 for level II and from 0.06 to 0.19 for level III. The hydrocarbon saturation reaches up to 0.88 for level II and up to 0.81 for level III. The net-reservoir thickness ranges from 50 to 101 m for level II and from 30 to 153 m for level III. The net-pay thickness ranges from 75 to 90 m for level II and from 22 to 110 m for level III. Maps show that the most favorable places for hydrocarbon reservoirs occupy southwestern part for Abu Madi level II reservoir and in the middle, the middle-west, the middle-east and the southeastern parts for Abu Madi level III reservoir.

Formation evaluation logoff results comparing new generation mining-style logging tools to conventional oil and gas logging tools for application in coalbed methane (CBM) field development

Acceptable data quality for formation evaluation forms the foundation for understanding the petrophysical and reservoir properties, coal quality and properties and pay zone identification. The petrophysical logs are used in both subsurface modelling and to optimise the well completion strategy, ensuring effective coal dewatering and desorption for gas production. At the moment, the industry common practice for data acquisition is to use open-hole wireline logging tools, which were developed primarily for the oil and gas industry. These tools are designed for higher pressure and temperature specifications compared to the reservoir conditions normally seen in coalbed methane (CBM), commonly called coal seam gas (CSG) in Australia. This results in heavier tools, larger logging trucks and increased manpower requirements than seen in mining logging operations.Arrow's CBM development projects in Queensland, Australia, are designed with a large number of wells (more than ∼1000 wells) that will need to be drilled and evaluated over the next ten years. At present, the cost of logging (direct wireline contractors and associated rig time cost) is forcing Arrow to choose between early data coverage (reducing project economics) versus restricted logging (increasing project risk). In order to resolve this issue, Arrow has embarked on a series of technology trials to investigate various cost effective formation evaluation solutions, while still ensuring data quality and operational safety.This paper will present the results of a comparison (log-off) of state-of-the-art mining stackable logging technology and conventional oil and gas logging technology. Also, the paper will focus on the mining-style logging technology data quality, equipment footprint, tool handling, calibration procedures, limitations and general operational efficiency.

Under-Rig-Floor Openhole Logging in the Gulf of Thailand: Operational Implementation of the Oil Industry's First Simultaneous Openhole Wireline Logging and Drilling Operation

Summary Chevron Thailand, on average, drills 12,000-ft measured-depth/8,200-ft total vertical depth wells in approximately 4.5 days. The factor that contributes most to this level of performance is the "offlining" of as many drilling-rig activities as possible. In our drilling operation, almost all pipe-handling and cementing operations are performed offline (i.e., off the critical-operations path and therefore simultaneous to other activities on the rig). We have now taken the next logical step in performing offline operations. In May 2007, Chevron Thailand introduced the world's first simultaneous openhole wireline logging and drilling operation on Seadrill RT-7 (a tender-assist drilling rig) and currently is deploying the same system on additional tender-assist rigs (TARs) and jackup rigs. This paper is the second in a series of two that describe the engineering design and operational implementation of the tools and techniques necessary to make offline openhole wireline logging a reality. The first paper (Upchurch and Graves 2008) in this series details the engineering design aspects, and the resultant benefits, of this paradigm-changing logging system. This second paper describes the processes that were used to implement the system, along with the inherent risks and benefits of each phase of the implementation. Implementing radically new processes such as this into pre-existing drilling systems significantly increases the risk for technical failure, well control incidents, and personnel injury. This paper details the processes that were developed for avoiding all three. In the case of this new technology, our phased approach to implementation has resulted in smooth, incident-free introductions to the various rigsites. The benefits of this new system, and our method for implementing it without incident, are paying significant dividends to Chevron Thailand.

Under-Rig-Floor Openhole Logging in the Gulf of Thailand—Engineering Design of the Oil Industry's First Simultaneous Openhole Wireline Logging and Drilling Operation

Summary Chevron Thailand, on average, drills 12,000-ft measured depth/ 8,200-ft total vertical depth wells in about 4.5 days. The factor that most contributes to this level of performance is the "offlin- ing" of as many drilling rig activities as possible. In our drilling operation, almost all pipe handling and cementing operations are performed offline (i.e., off the critical operations path and therefore simultaneous to other activities on the rig). We have now taken the next logical step in performing offline operations. In May 2007, Chevron Thailand introduced the world's first simultaneous openhole wireline logging and drilling operation on Seadrill RT-7 (a tender-assist drilling rig) and presently, is deploying the same system on additional tender-assist and jackup rigs. This paper describes the concept of offline openhole wireline logging and the engineering design of the components that make this new concept an operational reality. The paper also discusses the engineering required to integrate the unique offline openhole logging components with existing rig systems (for both tender-assist and jackup rigs). This complex integration of newly designed components with existing rig systems is the path by which Chevron Thailand is setting a new performance standard in offshore drilling. The benefits of this new system have proven to be significant in improving Chevron Thailand's already world-class drilling performance.

The Brenda field development: a multi-disciplinary approach

Ian F. Jones, Rod Christensen, Jamie haynes, John Faragher, Ika Novianti, Henry Morris, and Giles Pickering show how a multi-disciplinary combination of modern processing, imaging and inversion techniques can identify overlooked hydrocarbon prospects. Recent initiatives in the North Sea and UKCS such as the introduction of the Fallow Field initiative and offering of Promote licences have started to generate activity by attracting new entrants who can provide new capital and new ideas to focus on exploration and appraisal. Fields which had been abandoned, or considered of insufficient commercial interest, have been offered a new lease of life by allowing proactive companies to identify and exploit latent commercial prospects by tying in to existing infrastructure. Here, we showcase one such recent discovery, made by Oilexco, where a multi-disciplinary approach was taken to identify potential targets using state-of-the-art pre-processing and high resolution velocity model building and pre-stack imaging, combined with detailed calibrated reservoir attribute analysis based on elastic impedance inversion. This field could prove to be one of the largest finds in the North Sea for three years. Introduction Oilexco’s UK North Sea drilling programme on Licence P1042 (Block 15/25b) in the Outer Moray Firth, targeted oil in the Paleocene Upper Balmoral sandstone. Initially three wells were proposed: one on the structure previously drilled by the 15/25b-3 well, one on a structural high with classic four-way closure, and one on a channel sand feature, whose prospectivity was indicated by an anomalously low elastic impedance (EI) response on the far-offset stack. The surface location of the first new well, 15/25b-6 is approximately 150 m west of Conoco’s 15/25b-3 undeveloped discovery, which tested 2690 b/d of 39o oil from the Upper Balmoral sandstone from 20 ft of net pay in 1990. The 15/25b-6 well encountered the Brenda oil find announced by Oilexco on 26 January 2004. The well intersected a series of oil-bearing Paleocene Upper Balmoral sands, the thickest of which has 26 ft of high quality oil pay. In addition to this sand, several other thin bedded oil bearing sands were also intersected. The entire section was tested and yielded 40o API oil from the Upper Balmoral sandstone at an average rate of 2980 b/d, over an 18-hour test under stable flowing conditions, from 56 ft of perforations (evaluated with open-hole wire-line logs and formation fluid sampling tools). Associated natural gas flowed at an average rate of 600 million ft3/d throughout the test. No water or sand was produced during the test period. The surface location of the second well (15/25b-7) is approximately 4 km northwest of 15/25b-6. The vertical hole encountered ~ 50 ft of good quality Upper Balmoral sand which was logged as water bearing. The side-track (15/25b- 7Z) encountered another very porous clean Paleocene Upper Balmoral sand with a thin oil column at the top of the sand and a mud log gas response. The results of the well suggest that the Sheryl structure is separate from the Brenda oil accumulation which is at a structurally lower position. As a consequence, the well was abandoned. The third well, (15/25b-8) targeted the low EI anomaly. It was located 0.50 km west of the 15/25b-6 well, acting as an appraisal well to the Brenda oil accumulation. The well encountered 69ft of high quality oil pay in the Upper Balmoral sand, and also tested 40o API oil, but at rates up to 4785 b/d.

Abstracts: Comprehensive Reservoir Characterization Using Open-Hole Wireline Logs, Core, and Downhole Video, Buena Vista Hills Field, California 

Abstracts: Comprehensive Reservoir Characterization Using Open-Hole Wireline Logs, Core, and Downhole Video, Buena Vista Hills Field, California 

Stratigraphic Control and Formation Evaluation of Horizontal Wells With MWD

Summary. Sandstone reservoirs in the Gulf of Mexico typically do not form horizontal planes, and a predetermined course for a horizontal well cannot ensure that the well path will remain within the producing interval throughout the horizontal section. Detecting approaching bed boundaries and fluid contacts early enough to make the changes necessary to keep the well path in the producing interval is an important technical issue during the planning and drilling of horizontal wells. The first two horizontal wells drilled in the Gulf of Mexico achieved this objective with measurement-while-drilling (MWD) resistivity measurements and with supporting computer modeling for bed boundary detection. Introduction MWD propagation resistivity measurements can effectively detect approaching bed boundaries several feet from the borehole if there is a significant resistivity contrast between the two beds. In the well planning stage, the MWD log response can be modeled from the horizontal-well plan and data from offset wells. During drilling, the modeled log response can be compared with realtime directional and log data to monitor and correct the path as necessary. Finally, the MWD log and directional data can be used in postdrilling evaluation (1) to perform a petrophysical evaluation of the well, (2) to determine actual reservoir geometry, and (3) to plan completion and production strategies. Case histories illustrate how a combination of MWD measurements can be used to plan horizontal-well paths, maintain realtime stratigraphic control of the horizontal-well path, and evaluate the reservoir without requiring deployment of openhole wireline logs in the horizontal section. Background Texaco Eastern E and P Region has produced gas and condensate from deep reservoirs in the East Cameron (EC) Block 265 field, which encompasses EC Blocks 265, 278, and 283 in the Gulf of Mexico, 195 nautical miles southwest of New Orleans (Fig. 1). Three prolific gas sands were recognized in the field area northwest of Platforms A and B; however, platform placement relative to the shallow subsurface geologic structures made conventional development drilling and production in these three sands difficult. Recent technological advances in horizontal-drilling techniques made it possible to consider extended-reach, horizontal, or near horizontal wells as viable economic alternatives for producing these reservoirs; however, none of these methods had been attempted in the unconsolidated sediments common to the Gulf of Mexico. EC Block 265 field production history indicated probable water coning in one of these large gas reservoirs. A horizontal well was designed for this reservoir to reduce water coning by extending the drainage radius and reducing pressure drop at the wellbore/sand interface. After the horizontal-well plan was developed and the associated engineering issues addressed, two problems remained: how to predict accurately when the drill bit crossed the boundary between the shale bed and the objective gas sand below, and how to determine the location of the wellbore within the objective hydrocarbon section as drilling progressed. A full-service MWD tool was chosen to supply directional, gamma ray, and resistivity data for use in well-path monitoring, correlation with offset wells, and formation evaluation. The use of MWD technology provided a critical advantage: MWD modeling capabilities made it possible to predict tool response, and these predictions could be used as a guide during drilling. With data from offset wells, resistivity values in the objective reservoir were modeled for a 2-MHz MWD dual propagation resistivity (DPR) response at 87, 90, and 93 degrees angles. During drilling, these models were used successfully m combination with real-time data for well-path monitoring, offset well correlation, and stratigraphic prediction. Why Drill a Horizontal Well? A typical Gulf of Mexico field development and production plan begins with producing hydrocarbons from the deepest known stratigraphic reservoir and proceeding upward until the shallowest pay sands are fully exploited. Considering the development from each individual platform, the EC Block 265 field followed this general rule. After development drilling ceased on Platform A and two initial Platform B wells were drilled, Texaco elected to use a 3D seismic survey to evaluate the potential of additional fault blocks and deeper reservoirs in the EC Block 265 field. Platform B, set in 173 ft of water, was strategically placed to avoid penetrating shallow gas hazards en route to deeper objectives. The major difficulty of this development plan was to drain the shallow gas reservoirs properly without causing significant water coning. A horizontal or near-horizontal well was determined to be the best way to open up sufficient reservoir drainage footage and to reduce or eliminate JPT P. 1134⁁

Remaining-Oil Determination Using Nuclear Magnetism Logging

Summary The determination of the volume of remaining oil in a reservoir is a key ingredient in planning future oil recovery operations. Nuclear Magnetism Logging (NML™) is an openhole wireline logging method that can provide accurate estimates of remaining-oil volumes. The signal processing required to extract these estimates from the logging data and the NML logging procedures used in this application are the subjects of this paper. The physics of the NML method and the wellsite log-inject-log procedures used for remaining-oil determination is reviewed. The latter procedures include the doping of the mud with magnetite to kill the borehole signal and the injection of paramagnetic ions into regions sensed by the NML measurement to kill the formation-water signal. A new NML signal-processing algorithm for determining remaining oil is developed. The algorithm is an improvement over conventional envelope processing in low SNR environments. The algorithm explicitly accounts for the statistical properties of bandwidth-limited Gaussian thermal noise in extracting signal parameters from signal-plus-noise measurements. This is especially important for remaining oil determinations for which accurate estimates of both the fractional bulk volume of remaining oil, Vbro, and the uncertainties in these estimates are required. The method is applied to residual-oil data from a Shell well. The data consist of repeat waveforms at 44 stations. The FFFs are mostly in the range from 1.0 to 4.0 porosity units (p.u.) and the signal decay times are less than 50 msec. Thus, the data represent an abnormally difficult signal-processing problem as a result of the low SNR's. The results of processing these data are compared with results obtained independently by Shell with their own processing methods, which are widely regarded in the industry as standards. The volumes of residual oil and standard deviations estimated with the new signal-processing method developed in this paper are in excellent agreement with the results of Shell's processing methods.

Hydrocarbon Identification Using Mud-Log Chromatography in Low-Resistivity Simpson Sandstones: ABSTRACT

Oil-productive Simpson sandstones often exhibit very low resistivities, with little contrast to underlying aquifers. Modern log suites have improved interpretation, but wells continue to be drilled that defy accurate S{sub w} calculation. Traditional methods, using DSTs based on sample shows and mud-log gas increases, continue to be the rule; but they are expensive and allow only a crude estimation of fluid contacts dependent on the subjective judgment of the well-site geologist. At little or no additional cost, interpretation techniques incorporating mud-log chromatograph ratios can add considerably to reservoir knowledge, although better data quality than typically provided by Mid-Continent mud logging companies is required. Published methodologies were modified in this study to eliminate C{sup 5} (pentane) data because of measurement difficulties and to improve vertical resolution by shortening chromatograph cycle times. Mud-log ratio methods have been applied to a well in the Noble Northwest field of Cleveland County, Oklahoma, in which only one of three commercial oil reservoirs was identifiable with open-hole wireline logs. In all three cases, mud-log ratios remained very stable within the oil column, became somewhat erratic in the transition zone, then stabilized at different values in the water column. In the subject well, only the ratio methodsmore » predicted oil-water contacts consistent with structural relief and test results. One potential difficulty was the inability to recognize depletion/ a watered-out interval displayed ratios characteristic of productive reservoirs.« less

Gas Monitoring During Drilling Substantiates Hydrogen Occurrence and Eliminates Corrosion as Source: ABSTRACT

Chromatograms from the simultaneous use of 2 gas sniffers, one monitoring hydrocarbon gases and one monitoring H2, while drilling 5 uncased exploratory bore holes in Paleozoic rocks in Kansas substantiates that H2/N2-rich gas emissions are from the sedimentary rocks above the Central North American rift system and are not the result of corrosion of casing pipe. The gases extend over an area of more than 100 mi2, within which they appear to be migrating through formation waters along permeable zones at the silty to sandy base of pyritic shales. H2 was detected in various zones from ±500 ft depth in the Indian Cave Sandstone (Pennsylvanian) to depths of 2,100 ft in the Hunton Limestone (Silurian-Devonian). Negati e peaks (noncombustible), which overlapped the H2 positive peaks on the Wheatstone Bridge chromatograms, are thought to indicate N2 gas. Possible N2 gas occurs from about 1,300 to 2,100 ft, from the Heebner Shale Member (Pennsylvanian) to the Hunton Limestone. H2/N2 peaks on the chromatograms correlate well with the crossover peaks indicative of gas zones on open-hole wireline logs. End_of_Article - Last_Page 257------------

Evaluation of Wireline Down-Log Information and Effects of Increased Log Speeds on Data Quality

Wireline logs run in deviated Gulf of Mexico wells using new logging techniques are studied. Formation density and other logs can be recorded logging in or out of a hole at very high speeds and often provide excellent evaluation information. Down logs can be very useful in the event the usual up log becomes impossible. Increased log speeds may be justified in some cases involving hole problems or high rig costs. Introduction A study has been made of openhole wireline logs run in deviated wells in the Gulf of Mexico. Some new logging techniques of interest have been made possible by the introduction of computerized digital possible by the introduction of computerized digital surface logging units. Many of these techniques could not have been used previously due to limitations of the conventional analog surface logging units.Logs run going in the hole (down logs) often can provide valuable formation evaluation information, provide valuable formation evaluation information, particularly porosity data. Sometimes hole conditions particularly porosity data. Sometimes hole conditions are severe enough that the logs run coming up from total depth are not obtainable. Down-log porosity data often can distinguish hydrocarbon-bearing from tight zones and even oil from gas.Of particular interest is the observation that the formation density tool often can provide very good average porosity values when logged going in a deviated hole at a speed of 10,000 ft/hr with the caliper arm closed (Figs. 1 and 2). Down logs using other types of logging tools also have provided critical evaluation information.The accuracy of depth information is a problem, but zone thicknesses often are correct and depth errors can be estimated.The repeatability of various log types when run at speeds higher than normal also has been studied. Formation density logs run in high-porosity formations at 3,000 and 5,000 ft/hr show only minor variations from logs run at the conventional speed of 1,800 - ft/hr (Figs. 3 and 4). This excellent repeatability is due to the high gamma-ray count rates of the density tool in the offshore low-density formations of Pleistocene age. In fact, the variations observable between density logs run over a common interval in these low-density formations may be primarily a function of wall contact effects, not the primarily a function of wall contact effects, not the random statistical count rate variations. Statistics for the compensated neutron and gamma-ray devices relative to logging speed also are studied.Induction-type devices have been run at speeds up to 15,000 ft/hr with excellent repeatability using the computerized surface units.This paper is not intended to be a recommendation for increases in log speeds, particularly for the porosity devices. Increased formation density log porosity devices. Increased formation density log speeds in complex lithologies, for example, could reduce the value of the data greatly. JPT P. 1151