Managing complex brownfield production and sustainability expectations has become a norm in the oil and gas industry – where opportunities to materialize resources can still be present. This paper covers the constructive practices in Field B, a 50-year-old brownfield offshore Malaysia in understanding uneven fluid movements dynamics via execution of time-lapse data acquisitions to justify planning for infill drilling. This has led to successful four (4) horizontal geosteering well placement in the major oil reservoir units. Time-lapse contact monitoring was made possible through integration of recent open-hole, production, dynamic simulations & cased-hole saturation logs in Reservoir A. Between the year 2014 to 2021, saturation logging campaigns were executed, and phenomena of uneven fluid contacts was observed between the un-faulted western to eastern areas of the field. Eastern area wells have observed shallower gas-oil contact (GOC) and oil-water contact (OWC) by 80 to 100ft-TVD, resultant from gas and water injections, disproportionate production withdrawal, potential gas leaks behind casing and stronger aquifer strength. The combination scenarios of geological structure and fluid contact uncertainties provided a range to drive geosteering pre-job modelling planning to sensitize multiple cases to optimize the well trajectories. The integrated ranges of current contact derived from saturation logs, recent open-hole logs and reservoir simulation constructed the basis of low-base-high remaining oil opportunity cases for planning and economic evaluations. Coupled with advancement of frontier technology Geosteering-HD, four (4) wells successfully penetrated 35 to 80ft-TVD of oil column in horizontal section and maintained along 1500-2000ft-AHD. Tilted oil-water OWC was observed in three (3) of the wells located at eastern area, where the OWC trends shallower from the heel to toe of the horizontal portion confirming the results from time-lapse contact information and contacts prediction from reservoir model. The other well drilled at western area, observed a mostly flat OWC throughout the horizontal section with slight tilting towards the toe, reflecting weaker aquifer strength at the western flank as observed in recent cased hole and open hole logging. The fluid contacts and structure penetrated in all four (4) wells are within the predicted low-base-high cases from pre-job modelling, leading to an optimum placement of horizonal well in the oil column. These optimizations have led to a successful infill campaign, delivering higher production rates of 5,600BOPD against planned 4,600BOPD for brownfield reserves acceleration. All data acquisition needs to be exhaustively studied and managed as each holds an important piece of evidence on what the field tries to express. In this field, the timely execution of time-lapse cased-hole logs integrated with open-hole results were vital and principal driver in de-risking fluid contact uncertainties within eastern and western area prior infill drilling for a successful horizontal well campaign.

The horizontal wells within the context of this case study are located offshore Malaysia, where the reservoirs vary in grain size and quality. The infill wells include 3 oil producer wells targeting S reservoir and 1 horizontal sidetrack well targeting R1-R3 subunit reservoirs. The horizontal wells’ objective is to optimize minimum lateral length of 1,000-2,000ft MD at 1/3 vertical standoff from GOC within the target oil column. Based on recent data from offset wells, the fluid contacts (GOC and OWC) remained uncertain, hence well placement within the target oil column becomes the main challenge. The wells are expected to have low resistivity contrast between oil and water composition. In this kind of reservoir environment, the standard reservoir mapping tool may not be sufficient for differentiating reservoir fluid properties of oil and water bearing formation. For such challenging condition, an integrated real-time well placement technology, high tier triple-combo logs, Neutron Near- Far count and Formation Sigma measurements were deployed to fully achieve drilling objectives. 3 horizontal wells with 1 horizontal sidetrack well were successfully executed within the target zone, achieving objectives beyond expectation. A new generation of LWD tool including high-definition reservoir mapping-while-drilling technology with advanced inversion was deployed to fulfill geosteering requirements. The workflow presented in this project is a synergized scope of multi-domain, from both drilling and subsurface. This case study demonstrated the value of high-definition reservoir scale mapping technology. It provides an innovative and deterministic method to identify low resistivity low contrast boundaries of oil from transitional water zone which was difficult to be achieved by conventional reservoir mapping tool. At the landing section, the high-definition tool helped to reveal clearly OWC below the tool with greater confidence compared to the standard tool. The information from the high-definition tool, paired with the fluid identification offered from Neutron-Density and Neutron Near- Far count together were essential for an accurate landing. The usage of reservoir scale mapping technology in the horizontal section revealed the tilted OWC and reservoir structure at the same time, which allowed the team to achieve the required minimum production length while maintaining required standoff from the OWC. All wells were geosteered successfully with the accomplishment of placing the trajectories in optimum positions despite having a tight TVD window.

The scope of the paper is to share a case study of a successful horizontal well completed within an extremely thin oil rim of ~10ft with bottom water. This paper highlights the differentiating activities undertaken to deliver the well despite the challenges of extremely thin oil rim, strong water drive and uneven current fluid contacts. Prior to drilling this well, attempt was made to mitigate the uncertainty regarding the current gas-oil contact (GOC) and oil-water contact (OWC) by carrying out cased-hole logging in some of the adjacent wells, and re-sequencing and re-optimizing the location of two of the wells targeting the reservoirs below. This obviated the need for the pilot hole and thereby resulted in a cost saving of ~USD 1Million. Furthermore, the dynamic simulation model was updated to create a fit-for-purpose model with the latest OWC and GOC, so as to be able to test various trajectories. While drilling, the well was drilled with real-time reservoir mapping-while-drilling technology and integrated with real-time reservoir characterization, fluid typing and trajectory modification, while maintaining Dog Leg Severity (DLS) below 3 deg/100ft for the ease of completion run. Completion was then optimized with viscosity-based inflow control orifices. Post drilling, dynamic and well models were calibrated to the actual results to determine optimum production rate for the well life. The horizontal well was successfully navigated and optimally placed in the extremely thin oil column. Tilted contacts were encountered in the targeted subunits where actual current contacts came in ~20ft shallower at heel and ~10ft deeper at toe compared to prognosis. Consequently, the heel landed at a 5ft stand-off from water, and the toe landed 18ft stand-off from water and 6ft stand-off from gas. The well was successfully unloaded and tested at a controlled oil rate of 2887 bopd, 50% higher than planned target. This paper presents the entire process from well planning until well production tie-in. This was achieved through the integration of subsurface understanding with the utilization of the appropriate technology. Finally, the management's trust in the capability of the team members ensured deliverability of the target production rate and the consequent booked reserves.

The Teak Field is located 25 miles off the southeast coast of Trinidad in 190 feet of water, and has produced 250 million barrels of oil in its first 18 years since 1972. The original oil-in-place is estimated at 740 million barrels and daily production peaked at 58,000 BOPD (barrels of oil per day) in 1975. Production declined to a minimum of 29,000 BOPD in 1988, but rebounded to 34,000 B0PD in 1989, due to renewed 1989 development drilling which has yielded encouraging early results, and reversed an earlier fairly steep production decline. The Teak Field produces very high quality crude oil, API 30-35 degrees, from a series of clean, very fine-grained Pliocene quartz sandstones, occurring at sub sea depths between 4,000 and 12,000 feet. Porosities average 21-33 percent. Reservoirs are normally pressured, and drive mechanisms range from depletion-drive to strong water drive. Primary oil recovery factors are 17 to 65 percent. Individual reservoirs are 10 to 440 feet thick, extending across 100 to 800acres. The field is a large anticline within a regional wrench terrain, with fairly steep bed dips averaging 10 degrees. The geometry of the structure is considerably complicated by numerous cross-cutting normal faults which segment the field. Traps are arranged as stacked 3-way closures behind a major sealing fault. Recently continued field development has benefited from a team study approach, utilizing a geologist, geophysicist and reservoir engineer in a study group, to generate detailed structure maps and accurate reservoir models. The group worked in close cooperation with operations personnel. Case histories are included for two 1989 development wells, which were completed at a cumulative rate of almost 9,000 BOPD, about 25 percent of the total field rate. The A-6XX well was drilled to recover bypassed attic oil pay in a layered reservoir in the central part of the field, while the E-3X well was drilled to the south flank of the field as a high risk field extension into a previously untested and unmapped fault block. The success of these two wells illustrates the value of a team study approach in optimizing production from a mature oil field. These field studies are continuing at Amoco Production Company. INTRODUCTION This paper summarizes the history of Teak Field1, describes the various oil producing reservoirs, and discusses mature-field development strategy employed by Amoco since 1988, including brief case histories of two 1989 oil development prospects. The Teak Field is the fourth largest oil field in Trinidad, located 25 miles off the southeast coast in 190 feet of water (Fig. 1). Discovered by Amoco Production Company in 1969, Teak has produced 250 million barrels of oil and about 1 trillion cubic feet of gas from 1972 through 1989. Teak is a mature oil field with significant depletion after its first 18 years of production. Despite a steep natural decline rate of 25 percent per year, the field has responded favorably to renewed development drilling in 1989, and reversed a steady downward trend in production rate, achieving its highest rate in four years in January, 1990.

Wells 1A, 2A, 3A & 4A are designed as four (4) horizontal oil producers to maximize the oil recovery from the XXYY heterogenous sandstone reservoir in Offshore Malaysia. The reservoir has been producing since 1975 on natural depletion before gas injection (1994) and water injection (2019-2022) were introduced. XXYY reservoir is expected to have wide permeabilities ranges from as low as 1-mD to 4-D and high uncertainty of gas-oil contacts from recent saturation logging acquisition. Coupled with the complex reservoir nature of massive gas cap and thinning oil rim observed between 30-50ft-TVD, historical production of oil with optimum GOR in XXYY reservoir remained the main challenge towards late field life. For such challenging condition, pre-planning with multiple Autonomous Inflow Control Device (AICD) valve placement scenarios across the horizontal sections were analyzed using integration of reservoir and well models for valves optimization process to achieve well's target production and reserves by the end of PSC. Specific drawdown and production targets were set as critical design limits in managing sanding and erosional risks while still achieving production target. Ultimately, these models provided both instantaneous and long-term forecasts of AICD impact on the wells’ performance – key factors in the final design. The workflow presented in this project synergized scope of multi-domain from subsurface, completion and drilling. This case study demonstrates the value of detailed design steps on AICD placement across horizontal segments and optimizations based on actual open-hole logging interpretation, mainly – permeability, saturation and vertical stand-offs from gas-oil and oil-water contacts. The horizontal wells drilled are susceptible to "heel-toe" effect, resulting in dominant production in the heel section while the toe section contributes less, subsequently inducing gas coning at the heel. XXYY reservoir is also sand prone and requires sand control. For these reasons, all 4 wells are designed to be completed with Open Hole Stand Alone Screen (OHSAS) with the use of AICD to balance production withdrawal across the horizontal segments and provide GOR control. The four (4) wells penetrated 30-60ft-TVD of oil column with 10-15ft-TVD vertical stand-offs from gas-oil contact (GOC) to maintain a 2/3 column ratio from oil-water contact. Given these marginal stand-offs to GOC, integration of AICD sensitivities workflow were performed on-the-fly to analyze instantaneous and time-stepped oil and GOR rates allowing the team to achieve required production sustenance. The installations of optimized AICD have resulted in successful GOR control below 6 Mscf/stb targeted, resulting in delivering higher instantaneous production rates against planned of 4,600bopd. The success of AICD optimizations integrated with OHSAS completion, reservoir mapping and petrophysical evaluation have been proven as ultimate solution to deliver the wells oil production for a brown field rejuvenation project. The pre-drill and post-drill results calibrated to actual well tests are compared for further sensitivity analysis, to be used in the continuous improvement of production management strategies in the field.