The Jasmine Field is a mature stacked-sand oil field that has been on production since 2005. One of the biggest current challenges is to locate remaining oil accumulations. Seismic mapping, material balance and reservoir simulation studies provide pointers to promising locations, but can never guarantee accuracy. Pilot wells offer a means to appraise identified locations before committing to drilling horizontal wellbores. A pilot well is often used in Mubadala Petroleum drilling campaigns as part of an overall strategy to extend the field's life by continuing to locate and tap remaining oil accumulations. Collaboration across subsurface teams leads to decisions on pilot well locations. In most cases the pilot well appraisal objectives will be to confirm the structural position, to identify fluid contacts or to assess depth uncertainty, especially in areas where there is no well penetration or in significantly updip locations. These appraisal objectives apply to shallower and deeper horizons as well as to the target reservoir itself, and in Jasmine there is a strong record of accomplishment of successfully locating remaining oil by means of such appraisal. It is critical therefore, that well planning is tailored so as to accommodate the appraisal objectives as well as the eventual production target. Two case studies are presented, illustrating different approaches to using pilot wells prior to placing horizontal wellbores in Jasmine field. In the first case, the horizontal production wellbore was planned to develop an updip region of the target reservoir, to access remaining oil, with additional pilot well appraisal objectives in both shallower and deeper zones. The location for the new horizontal well was confirmed and this dual-role pilot/producer well not only succeeded in reducing depth uncertainty for the new horizontal wellbore, but also identified additional reserves in other reservoirs. In the second case an appraisal pilot well was used to investigate a downdip region of a depleted reservoir. Material balance assessment had indicated that the volume accessed by the updip producer was larger than suggested by the static model, which might have resulted in water encroachment from downdip, causing the appraisal location to water out. However, seismic imaging identified potential barriers between the updip and the proposed downdip appraisal location, which would have prevented water encroachment from downdip. The pilot appraisal well was required to distinguish between those two possibilities.

We present the results of a 3D fault-seal analysis across the central part of the Jasmine Field, Gulf of Thailand. Two techniques were applied; a stochastic juxtaposition analysis across thin, stacked, laterally variable reservoirs and then a comparison of fluid contacts and reservoir capillary pressure against predicted fault clay content. The two methodologies can be compared to better understand how they provide insights into reservoir behaviour. Our objective was to estimate capillary threshold pressures for fault-seal calibration in exploration prospects in the Gulf of Thailand. First, the stochastic juxtaposition analysis workflow evaluated whether known oil/water contact (OWC) levels in the key reservoir intervals could be explained by crossfault juxtaposition patterns. Second, modeling was used to calibrate fault capillary threshold pressure against predicted fault clay content. Fault clay content is estimated from the shale gouge ratio (SGR) and compared to the reservoir capillary pressure estimated from known OWC levels and fluid densities for each reservoir interval. The maximum capillary threshold pressure for a given clay content can be estimated and calibrated to trend curves for fault seal across the basin. For 12 key reservoir zones examined, stochastic juxtaposition analysis cannot explain observed OWC levels by crossfault juxtaposition for all reservoir intervals. Therefore, control by structural spillpoints and/or capillary membrane sealing across faults is required. Estimated capillary pressure information is combined with measured mercury-air capillary threshold pressure from Jasmine A reservoir samples and published data to create clay content-capillary threshold pressure curves to estimate fault-sealing capacity across the Jasmine Field. The results can be applied to other fields and prospects in the Gulf of Thailand. Fault-seal analysis and estimation of fault properties in areas with multiple stacked, laterally variable reservoirs is notoriously problematic because of the large uncertainties involved. Our approach of stochastic juxtaposition analysis combined with capillary pressure modeling allows the uncertainties to be addressed while providing concise and usable input to decision-making.

Greater Sirikit East (GSE) Field represents recent step-out exploration success in the east of Sirikit Main Field. Sirikit Main was discovered in 1981 and remains the largest field in the basin, with surrounding smaller fields: Sirikit West (northwest, 1983), Thap Raet (north, 1988), Sirikit East (northeast, 1992) and Nong Jig (southwest, 1999). GSE comprises of multiple blocks defined by structural and stratigraphic closures. It shares common reservoir and source rock with Sirikit Main. Some of the trap types and seals are also common. However, some trap types and seal elements are not typical in Sirikit Main. More detailed subsurface evaluations were conducted to explore all the working petroleum systems. This is the key and challenge to the GSE that had been overlooked in the past due to the absence of considerable structural closure in the key horizon maps. Aggressive step-out exploration in GSE started in 2006. More than 12 exploration/delineation wells have been drilled to date testing multiple blocks and plays. The exploration concepts have been continuously developed by taking the feedback from the well post drill evaluation. The new developed or refined concepts were then applied to the subsequent exploration/delineation drilling. This cycle allows better risk mitigation as well as more accurate well targeting. To minimize exploration cost, time and risk, following strategies have been adopted whenever feasible: To use existing drilling surface location, to combine multiple targets and to provide back-up side-track target. Utilizing existing surface location made significant time and cost saving by avoiding costly land acquisition, access road building and time-consuming environmental impact assessment. Continuous exploration and delineation drilling in 5 years has changed the GSE area. The previously overlooked large area that looks like a monocline in main marker maps turned out to hold multiple hydrocarbon accumulations involving both stratigraphic and structural traps. Introduction Greater Sirikit East Field is located just to the east of the Sirikit Field in the S1 concession, Phitsanulok Basin (Figure 1), Central Plain Onshore Thailand, approximately 400 kilometers north of Bangkok. The concession is 100% owned and operated by PTT Exploration and Production. Sirikit Field was discovered in 1981 and remains the largest field in the basin. Up to 2000, 5 adjacent smaller fields have been discovered. Sirikit West Field in the northwest was discovered in 1983. Thap Raet Field in the north, discovered in 1988, Sirikit East in the Northeast, discovered in 1992, Nong Jig oil in the southwest, discovered in 1999, and Nong Pluang gas in the south-southwest, discovered in 2000. The first-discovered Sirikit Field is normally called as Sirikit Main Field in order to distinguish it from the neighboring fields bearing 'Sirikit' name.

Greater Sirikit East oil and gas field is located just to the east of the Sirikit Main field in the S1 concession, Phitsanulok Basin, Thailand. The main reservoirs are fluvio-deltaic Lan Krabu formation members of K, L and M that interfinger with the open lacustrine Chumsaeng formation. Hydrocarbon traps in the field can be grouped into structural and stratigraphic traps. Numerous small structural closures have been proven to be hydrocarbon bearing. Delineation and development well drillings have also proven the working stratigraphic trap system in the absence of structural trap. In some structural closure, observed hydrocarbon column heights from well data exceed their relevant structural spill point, invoking the larger working stratigraphic trap system responsible for the hydrocarbon accumulation.Various examples of proven stratigraphic traps in the field will be presented in this paper. Structural maps, well correlation, pore-pressure plot, production data and existing internal studies on sequence stratigraphy and reservoir facies were incorporated in this evaluation. Reservoir characterization from seismic data is not considered feasible due to resolution limit. Most of stratigraphic traps are within the distal sub-members of Lan Krabu Formation such as M, L2, K4, K2 and K1 which are dominated by mouthbar facies. The trapping is formed by combination of deposition and structure geometries. The structure is East-Northeast dipping, while the depositional direction is from the Northwest to Southeast direction. A trap system is hence formed where reservoir sand pinch-out to the southeast direction that is structurally up-dip, bounded by north-south trending fault in the west.

Central Faulted Region (CFR), East Flank Region (EFR), and Greater Sirikit East (GSE) are the main production areas in the PTTEP S1 Consession, part of Sirikit Field, the biggest onshore oil field in Thailand. The Lan Krabu Formation is the biggest contributor for hydrocarbon production, defined as a thick fluvio-lacustrine deltaic sequence consisting of thin alternations of mouthbar deposits, channels and Chum Saeng lacustrine claystone. The CFR, EFR and GSE regions are structurally complex, each of which is separated by west dipping, basement rooted main fault. The secondary faults are east dipping antithetic and west dipping synthetic faults which run almost parallel to the main fault. For modelling purposes, detail geological correlation across CFR, EFR and GSE has been established. The correlation utilizes the sequence stratigraphy concept by correlating the flooding surface of the fifth order sequence. The shale interval associated with fifth order flooding surface may inhibit vertical pressure communication or vertical oil movement during production time frame. Given the highly heterogeneous reservoirs in fluvio deltaic environment together with complex faulting system, it is very challenging to build a geological model that represents the detailed geological features of these areas. Selecting the 3D modelling tools is essensial to generate a model with complicated geological features, in a way that reservoir simulation can be performed in an efficient manner. This paper will share challenges prior to and during construction of the 3D geocellular model, as well as various modelling approaches that have been generated with multi-scenarios and multi-realizations tasks. It also demonstrates how pixel, object and multi-points statistics (MPS) based approaches in facies modelling along with the application of continuous and discrete N/G provide alternative input for the reservoir modelling. The result of this study will be used for flow performance evaluation and further dynamic modelling. Introduction Sirikit Field is located in Phitsanulok Basin, Central Plain, onshore Thailand, approximately 400 km north of Bangkok (Figure 1). The Field is the country's largerst onshore oil field located in the S1 concession, currently operated and wholly owned by PTT Exploration and Production. The Field was discovered in 1981 by LKU-A01 well drilled by TSEP (Thai Shell Exploration and Production). In effort to increase the oil recovery, Waterflood has been implemented within the Sirikit Area. The East Flank Region was the first region to be waterflooded starting in 1995. The EFR was selected for a waterflood candidate based on the fact that it had the least amount of faulting among the regions. Water injection in Central Faulted Region just started end of 2010. The Greater Sirikit East is a relatively new area, discovered in 2006, and it is still producing under primary recovery.