The Marrat reservoir in Dharif field is a deep, sour, high pressure oil accumulation of Jurassic age containing light under-saturated oil of 36-380 API. The carbonate reservoir has a porosity range of 10-20% with permeability of 1-10 md. The field was put on production in 1989 through one well. Subsequently, 10 wells were added gradually developing the field. As of date, the field has produced about 12.5% of oil in place, lowering the reservoir pressure from 10,525 to 7,000 psi.
At present, oil production from the field is about 13,500 bbls/day. Due to low permeability, some wells produce with high drawdown approaching asphaltene onset pressure (AOP), estimated at 3,400 psi. This causes Asphaltene deposition in the tubing that requires cleaning to maintain the production level. The major challenges now are to produce the wells above AOP to avoid asphaltene precipitation in the wells or reservoir while sustaining the production level and maximizing recovery.
Hence, Full Field Model (FFM) for simulation studies was constructed and history-matched. Under depletion case, where the wells produce above AOP, field produced about 24% STOIIP. The water injection case shows significant increase in recovery to 40% STOIIP. Since no prior experience of water injection is available for such tight deep carbonate reservoirs in West Kuwait Fields, several key studies such as a) RCAL & SCAL b) Core flood Study c) Water Compatibility & Scale Prediction modeling d) Injectivity test, were carried out to address water injection feasibility.
The present paper shares the results of above studies which indicate that water injection is a viable option to maintain the reservoir pressure to produce the wells above AOP as well as to maximize recovery. Pilot water injection is planned through one well for which the area has been optimized using FFM. At present Pilot Water injector and source wells have been drilled and injection will be initiated with commissioning of surface facilities
Dharif field is NNE trending elongated anticlinal structure with faulted western limb. The Marrat reservoir in this field has developed in carbonate aggradational and progradational depositional setting. The field was discovered in 1988, put on production in 1989 and gradually developed with additional producers until 2004 (Fig-1). As of today, total 13 deep wells have been drilled in this field of which eleven are completed in the Marrat reservoir, while two are completed in a shallower Jurassic reservoir. The reservoir porosity ranges between 10-20 % while the average permeability is low, ranging between of 1-10 md with locally higher permeability of about 20 - 30 md in some layers. The average net reservoir thickness is about 200 ft and water saturation is less than 15 %. Initial oil water contact (OWC) was estimated to be 13,360 ft Subsea. The initial reservoir pressure was 10,525 psi at 13,200 ft SS (datum). The oil is under saturated with saturation pressure as 1,959 psi. Oil is light and the density is 36-380 API. The asphaltene onset pressure (AOP) is nearer to 3,400 psi, at a temperature of 2350 F.
Gezeeri, Taher Mohd Nabil (Kuwait Oil Company) | Hamim, Ahmed Ibrahim (Kuwait oil Company) | Zereik, Rachad (Halliburton) | Hughes, Simon Nicholas (Halliburton Sperry-Sun Drilling Services) | Scheibe, Christian (Halliburton sperry sun drilling services)
The Upper Cretaceous Mishrif reservoir in Minagish field is currently being developed by Kuwait Oil Company (KOC) using a horizontal drilling program. The Mishrif reservoir is approximately 300 ft thick across the field, with an average net pay of 170 ft in the upper layers. The reservoir porosity varies from 15 to 30%, and permeability ranges from 0.001 to 17mD. The first Mishrif horizontal well was drilled from west to east in the northern block of Minagish field. The well appears to have penetrated several generations of faults and associated fractures (early northwest to southeast, intermediate northeast to southwest, and possible late northwest to southeast. The production rate has been poor (approximately 500 bbl oil per day). An evaluation of the image logs indicated that only two of the reservoir layers appear to be fractured, whereas other layers are muddy and devoid of fractures, even near faults. To address the structural and stratigraphic uncertainties of the Mishrif reservoir, a high-resolution elemental chemostratigraphy study was performed on cored wells prior to additional drilling. The study produced a robust elemental zonation primarily based on variations in CaO/MgO, CaO/Sr, and MgO/Sr (carbonate-related), SiO2/Al2O3 and Zr/TiO2 (detrital-related), and Br, S, Na2O, and Cl (diagenetic phases and/or formation waters). The study results were used to calibrate a portable laser-induced breakdown spectroscopy (LIBS) instrument, which was used for near real-time chemostratigraphy at the wellsite to assist in geosteering operations. The recent horizontal well penetrated a highly faulted section in Mishrif layer 2, with significant changes in dip related to faults. LIBS technology assisted in actively optimizing the well path in the porous limestone zone, only 5 to 10 ft thick, within this structurally complex regime. The distribution of possible fracture swarms and faults was reflected by abrupt changes in the geochemical profiles (MgO/CaO, S, [Ni+V+Fe2O3]/Al2O3, Na2O, and Cl). This well achieved a new record for the longest horizontal drain hole in Kuwait.
Al-Marri, Salem Sml (Kuwait Institute for Scientific Research) | Alkafeef, Saad F. (College of Technological Studies) | Chetri, Hom B. (Kuwait Oil Company) | Al-Ghabdan, Asma'a (Kuwait Oil Company) | Al-Anzi, Ealian H.D. (Kuwait Oil Company)
Reservoir souring while water flooding North Kuwait reservoirs has been predicted by modeling studies in the past. One of Sabiriyah Mauddud wells showed up H2S as first indication of reservoir souring, which was an alarm bell for production facilities designed for only sweet crude. Surface/ Bottomhole fluid samples were required to confirm whether it is localized or reservoir-wide. In order to track reservoir souring and monitor on continuous basis, a process for tracking of reservoir souring annually was developed and initiated for the first time in 2006. Subsequently, this has been made part & parcel of fluid study requirements each year.
As sea water is being injected into traditionally sweet reservoir like Sabiriyah Mauddud, some degree of reservoir souring is expected due to Sulfate reducing bacterial (SRB) activity, as was projected happen sometime in 2005 in wells, needing monitoring/ mitigation actions. Expected H2S levels being very low (50-200 ppm), risk of loosing and not capturing these concentrations using conventional samplers/ bottles due to absorption/ reaction with the metallurgy of the samplers was felt, thus posing a challenge for obtaining a representative bottomhole sample for the analysis of H2S.
A comprehensive sampling program was made jointly by KOC & KISR, using the non-reactive internally coated samplers for capturing bottom hole samples; performing the onsite analysis, followed by immediate shipment to the local fluid analysis laboratory and conduct all necessary analysis with expert supervision & care.
Value was added to North Kuwait Water flood management by timely knowing the onset of reservoir souring. The analysis also led the way forward for the review of chemicals dosages; interventions needed in case of H2S occurrence; inputs to the future facilities and the requirements of further modeling studies.
Sabiriyah Mauddud, a super giant depletion drive oil reservoir in North Kuwait, is undergoing massive development efforts, with a planned enhancement in oil production through phased pattern water flood. The Phase1 development covers the crystal area of the structure, which is the focus for current development efforts through twelve number of inverted 9-spot water flood patterns.
Al-Sulaiman, Saleh (Kuwait Oil Company ) | Al-Mithin, Al-Sulaiman Wahab (Kuwait Oil Company) | Murray, Grant (Maersk Oil ) | Biedermann, Murray J. (Corrpro Companies Inc. ) | Islam, Moavin (Corrpro Companies Inc. )
Kaufman, R.L. (Chevron Overseas Petroleum) | Kabir, C.S. (Chevron) | Abdul-Rahman, B. (Kuwait Oil Company) | Quttainah, R. (Kuwait Oil Company) | Dashti, H. (Kuwait Institute of Scientific Research) | Pederson, J.M. (Chevron) | Moon, M.S. (Chevron)
This paper describes recent results from an ongoing geochemical study of the supergiant Greater Burgan field, Kuwait. Oil occurs in a number of vertically separated reservoirs including the Cretaceous Third Burgan, Fourth Burgan, Mauddud, and Wara. The Third and Fourth Burgan sands are the most important producing reservoirs. Over 100 oils representing all major producing reservoirs have been analyzed using oil fingerprinting as the principal method, but also supported by gravity and sulfur measurements.
From a reservoir management perspective, an important feature of the field is the approximately 1,200-ft long hydrocarbon column which extends across the Burgan reservoirs. Oil compositions vary with depth in this thick oil column. For example, oil gravity varies in a nonlinear fashion from about 10 API near the oil-water contact to about 39 API at the shallowest Wara reservoir. This gravity-depth relationship makes identification of reservoir compartments solely from fluid property data difficult. Including oil geochemistry in the traditional mix of PVT and production logging data improves the understanding of compartmentalization and fluid flow in the reservoir, both in a vertical and lateral sense.
The composition of reservoir fluids is controlled by a number of geological and physical processes. We attempted to identify unique sets of geochemical parameters that were sensitive to specific oil alteration processes. One set of geochemical properties correlated strongly with gravity and is therefore related to the gravity-segregation process. A second set of parameters showed essentially no correlation with gravity or depth but established unique oil fingerprints for most of the major producing reservoirs and identified a number of different oil groups within the Burgan and Wara reservoirs. We interpret the presence of these oil groups to indicate reservoir compartments owing to laterally continuous shales and faults, which act as seals on a geologic time frame. Compositional differences between groups of oils arise from the reservoir filling process. A third set of parameters correlate with water washing and/or biodegradation processes, indicating oil alteration during production. We are investigating these parameters to determine if they can identify production-time-frame barriers. The geochemical data were integrated with PVT-data for better understanding of the fluid distribution.