Resolving Development Strategy by Integrating Geophysical, Geological and Pressure Transient Test Data: A Case Study of Heterogeneous Lower Eocene Sand of Upper Assam Basin, India
Abstract: TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA multi-disciplinary approach had been adopted to resolve the exploitation and development strategy for Deohal and its extension oilfield having mainly the deep Eocene clastic reservoirs which is geologically complex, over pressurized stack of thin sands [by 30-40 Kg/cm 2 (assuming 0.1 Kg/cm 2 /m hydrostatic gradient] interbedded with shale/ carbonaceous shale. An accurate delineation of individual sand in such reservoirs is beyond the resolution of seismic a… Show more
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Daqing, the largest heterogeneous multi-layer none marine reservoir oilfield in China celebrated its 45thbirthday in Ocotober 2005. Boasting 27 continuous years of plateau oil production over one MMBOD, the largest industry polymer-flooding oilfield in the world, and excellent developing effect, its development strategies and techniques applied provide a road map to maximize oil recovery:Life cycle reservoir studies give insight into reservoir, and providea foundation for plan of development, implementation of infilling, and associated workover jobs such as zonal stimulation, zonal waterplugging.Early reservoir pressure maintenance by internal water flooding maintains reservoir pressure close to its original status, providing sufficient reservoir energy, enabling high and stable production rate for a long period as well as improving recovery.Performance monitoringconducted in the whole process of development, of which, separate layer performance monitoring is one of the most important foundation for in-depth understanding subsurface development potential.Pilot tests are conducted before any key development strategies and measures are applied to ensure their success.Separate layer production/water injection of multi-layer and heterogeneous reservoir and novel completion are the key measures for enhancing poorly drained reservoir water flooding, improvingits sweeping efficiency.Multi-time and progressive infilling drilling develops bypass oil resulting fromthe geological complexities of reservoirs.Widely applying polymer flooding enhances oil recovery by over 10%.Innovativetechnology makesdevelopment of marginal reservoirs/fields economical. Outstanding development of the giant field has proven the validity of above strategies and techniques with an oil recovery factor current at over 51% in the main block. Introduction Major challenges facing petroleum industry are to maximize recovery for a mature asset, extend the life of traditional producing areas, to optimize development of a new field as new reserve becomes increasingly complex. The average conventional crude oil recovery quoted in petroleum industry is 35%. However, a 10% incremental recovery translates to about 1.4 trillion barrels of recoverable resources, or roughly an additional 50-year supply of global crude consumption at current rates (Saleri, 2006). The estimate reminds us that there are vast potential resources of hydrocarbons in the world thatare waiting for new technology to tap them. Numerous efforts focusing on matured assets aiming at finding new oil in old reservoir and revitalizing old-field have been made. These efforts emphasize the importance of application of integrated approaches or multidisciplinary reservoir management. However, maximizing oil recovery is not only a system engineering, but also lifecycle process running through various stages of oilfield development from initial development, production increasing and reaching its plateau, to production declining as the oil field reaches the mature state of its development.
Daqing, the largest heterogeneous multi-layer none marine reservoir oilfield in China celebrated its 45thbirthday in Ocotober 2005. Boasting 27 continuous years of plateau oil production over one MMBOD, the largest industry polymer-flooding oilfield in the world, and excellent developing effect, its development strategies and techniques applied provide a road map to maximize oil recovery:Life cycle reservoir studies give insight into reservoir, and providea foundation for plan of development, implementation of infilling, and associated workover jobs such as zonal stimulation, zonal waterplugging.Early reservoir pressure maintenance by internal water flooding maintains reservoir pressure close to its original status, providing sufficient reservoir energy, enabling high and stable production rate for a long period as well as improving recovery.Performance monitoringconducted in the whole process of development, of which, separate layer performance monitoring is one of the most important foundation for in-depth understanding subsurface development potential.Pilot tests are conducted before any key development strategies and measures are applied to ensure their success.Separate layer production/water injection of multi-layer and heterogeneous reservoir and novel completion are the key measures for enhancing poorly drained reservoir water flooding, improvingits sweeping efficiency.Multi-time and progressive infilling drilling develops bypass oil resulting fromthe geological complexities of reservoirs.Widely applying polymer flooding enhances oil recovery by over 10%.Innovativetechnology makesdevelopment of marginal reservoirs/fields economical. Outstanding development of the giant field has proven the validity of above strategies and techniques with an oil recovery factor current at over 51% in the main block. Introduction Major challenges facing petroleum industry are to maximize recovery for a mature asset, extend the life of traditional producing areas, to optimize development of a new field as new reserve becomes increasingly complex. The average conventional crude oil recovery quoted in petroleum industry is 35%. However, a 10% incremental recovery translates to about 1.4 trillion barrels of recoverable resources, or roughly an additional 50-year supply of global crude consumption at current rates (Saleri, 2006). The estimate reminds us that there are vast potential resources of hydrocarbons in the world thatare waiting for new technology to tap them. Numerous efforts focusing on matured assets aiming at finding new oil in old reservoir and revitalizing old-field have been made. These efforts emphasize the importance of application of integrated approaches or multidisciplinary reservoir management. However, maximizing oil recovery is not only a system engineering, but also lifecycle process running through various stages of oilfield development from initial development, production increasing and reaching its plateau, to production declining as the oil field reaches the mature state of its development.
Integrated Reservoir Characterization and Approach for Improving Development Drilling of Narrow Fluvial Channel Reservoir within a Thin Oil Rim
By integrating geological, seismic data, geochemical mud log data, wireline log correlations, DSTs, reservoir/production data and 3D modeling; a detailed reservoir characterization was conducted in a narrow fluvial channel reservoir within an oil rim. Application of acoustic impedance (AI), generated from 3D seismic inversion, proved to be an effective measure for identifying subsurface sandbody/coal from shale. The sum of negative AI values showing single sandstone in local well region as well as whole sandstone within an oil column was mapped. This provided a sound base for identifying reservoir targets and designing the proposed well to optimally penetrate multiple targets. During drilling, geologist and geophysicist cooperated together on carrying out a "real time" reservoir study, where the geological model was revised in time, allowing the application of sidetracking a well to improving the successful drilling. Results of integrated reservoir characterization, in particular the application of AI, have greatly improved the success of development drilling for narrow fluvial channel reservoirs within oil rim. Introduction The NE Betatra Field, Sumatra, Indonesia, discovered in 1995, is a highly faulted low-relief anticlinal rollover bounded by faults to the east, west and south above an inverted graben. The primary productive intervals are an oil rim and gas cap within multiple Lower Talang Akar Formation (LTAF) at depths between 4,361 feet subsea and 5,361 feet subsea. Originally 12 wells were drilled in this field. Results suggested that reservoir distribution varies dramatically across the field. Ggeneral reservoir characteristics can be summarized as follows:Reservoirs have large gas caps and a small oil rim with a thin oil column. The field covers more than 122km2, with a maximum hydroncarbon column of more than 1000 feet. Howerver the oil column is 30 to 35 feet thick;Numerous major faults and sub-faults result in a complex structural framework. Based on the faults and trends of faults generated from 3D seismic, 7 areal compartments (fig.1) have been identified. In turn, hydrocarbon and water contacts in each compartment varies resulting in complex fluid distribution;Reservoirs are narrow fluvial meandering channel sandbodies. The 30% value of RNG indicates the fluvial channel sandbodies are lack of amalgamation;Reservoir CO2 content has a large degree of variability indicating complex distribution throughout the field. Analysis of gas from several DSTs per well shows that CO2 content does not vary with depth. CO2 content averages 15% in the west to 55% in the east of the NEB Field. This indicats CO2 migration is along bounding faults in the east from a source of CO2 generation. The above characteristics present major challenges. The variability of fluid contact as well as CO2 content suggests the complex and compartmentalized nature of Northeast Betara Field. Reservoirs are compartmentalized by a lack of communication both laterally due to lack of amalgamation of the channel meander belts and vertically due to vertical permeability barriers. Small oil rim, narrow oil-bearing sand widths and structurally complicated blocks demand an integrated approach for effective reservoir characterization and innovative development strategy to improve the drilling success rate and ensure maximum recovery. Integrating the geological, seismic, reservoir/production data, geochemical mud log evaluation and 3D modeling have conducted reservoir characterization. Utilization of integrated reservoir characterization, coupled with the ‘real time’ geological model revised during drilling resulted in 14 wells that successfully penetrated hydrocarbon-bearing sands. Eleven wells encountered both gas and oil-bearing zones within an oil column, including 2 successful sidetracks that encountered 14 ft and 30 ft of oil pay.
Makmur Field, South Sumatra, Indonesia, is a faulted anticlinal rollover with its major mutli-layer reservoir of distributary mouth bar, delta front sheet, and sub-aqueous channel sand. The field reached its production peak at end of 2001. In order to hold back the bottom or peripheral water encroachment, arrest promptly production declining, and ensure the maximum final recovery, integrated reservoir characterization including detailed microfacies and structure mapping, 3D geostatistic modeling, and subsequent reservoir simulation coupled with routine drainage radius analysis have been conducted. Meanwhile, pressure build-up test and production monitoring were optimized and selected performed. The effective reservoir management including development infilling, optimized well sidetracking, dual string well completion, gas lifting, active workover operation, as well as drilling of injector and optimization of facility utilization for water injection enhancement has been implemented, which provided a road map for improving the field development. Application of the integrating reservoir management techniques resulted in substantial added reserve and mitigated pressure dropping. The successful infilling and water shut in workover have obviously arresting production declining rate. Introduction Located in Jabung Block, South Sumatra, Indonesia, Makmur Field is a faulted anticlinal rollover with major production from middle Miocene Air Benakat and Gumai reservoirs. In its discovery well Makmur-1, Air Benakat and Gumai tops are found at depths between 3,620 feet and 5,070 feet subsea. The field is bounded to the north by a major east-west fault that was responsible for trapping hydrocarbons (Figure-1). Gumai and Air Benakat reservoirs mainly consist of distributary mouth bars, delta front sheets, and sub-aqueous channel sands, deposited in a regressive distal delta front to marginal marine fluvio-deltaic environment and periodically interrupted by subtle transgressive events. The main producing reservoir in Makmur is the A37 sand. Geological correlation and interpretation has sub-divided the sand into 5 layers within the reservoir designated as A37.1, A37.3, A37.5, A37.7 and A37.9. Three marginal reservoirs are G50B, G52A and G52B sands. Makmur Field commenced production in January 1998. By July 1998, 7 wells were producing (6 wells from the A37 reservoir and 1 G52B completion). During 2000 and 2001, another 7 wells (Mk-8, Mk-9, Mk-10, Mk-11, Mk-12, Mk-13, Mk-14) were drilled. Mk-10 tested the southeast extension of the field and produced 14,610 barrels oil before quickly going to water. Mk-10 was converted into a water injector to supply pressure maintance for the A37.7 sand. Field production reached a peak of 12,000 barrels per day in December 2001. Since that time the field had experienced a sharp decline in production. In order to optimize reservoir management, arrest the steep production decline, improve final recovery, and extend the fields economic life, an integrated reservoir characterization study was conducted.This study incorporated additional wireline data from the seven (7) new wells, well production performance and available PLT data. This study consists of detailed reservoir correlation, microfacies and structure mapping for each correlated single depositional unit, net pay and net porosity distribution, 3D stochastic modeling, single well and field production analysis, drainage radius analysis and streamline simulation. In addition, a complete reservoir simulation was implemented. The above study presented major challenges for development of Makmur Field:Reservoir voidage caused by shortfall of water injected resulting in obvious pressure decline demands reservoir pressure maintenance;Reservoir heterogeneities resulting from various petrophysical properties caused unbalance inter-layer water flooding which by-passed oil in relativily poor reservoir layers;Due to relative large inter-well distance and geological complexities, some inadequate drainage or by-passed reservoir sand, made it necessary to drill addtional wells.
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