Well testing provides useful data for reservoir characterization during various stages of field life, from exploration, development to production. The key information that are typically can be obtained are, information on reservoir properties, deliverability, and pressure data. However, if the data acquisition during the well testing is compromised it can also lead to incorrect data and could lead to a wrong understanding of the reservoir and could results in sub-optimal field development. Therefore, it is important to emphasize on the quality of the data being acquired. This paper captures the experiences gained for a high-pressure-high-temperature (HPHT) exploration well DST where data acquisition was compromised in the 1st well drilled in the structure. A combination of temperature transient effect and tubing movement in the well during shut in resulted in data quality which can't be interpreted with confidence. The lessons learnt from the same was captured and addressed successfully in the subsequent well which enabled quality data acquisition. The objective of this paper is to share the challenges and mitigation strategies for a HPHT DST with the help of two DST operation where the challenges resulted in less-than-optimum data quality and the one where they were mitigated. The range of challenges came from planning, to gauge placement, to identify potential problems early, and even having proper contingency plans to cater for unplanned events. The paper also deals with some of the best practices which can help with any DST program. Key examples are pre-job modeling, accurate temperature measurement and modeling, real-time data acquisition, and a special focus on sampling as a part of a successful DST program. Disclaimer All parameters cited in this paper are purposely made in ambiguous manner to maintain confidentiality of the data.

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.

Mini-DST, as alternative to conventional DST, has been in the industry more than 30 years, and its economic value has showed the advantage over DST, however limited permeability-thickness and investigated radius is a bottle neck which in many cases has much uncertainty to support reservoir characterization. The recently developed Deep Transient Testing technology improved its performance over former mini-DST technology in terms of longer pumping time, larger produced volume, and greater investigation radius. This paper presents a study in a variety of environments and applications, demonstrating how formation testing is being planned, acquired, and used in new ways, including Deep Transient Testing (DTT). The comprehensive radial model approach based on DTT using integration of well logs, numerical simulation grid and pressure transient behavior is built for the first time. To design an effective approach to generate a radially gridded single well predictive model, this workflow requires knowledge of well performance, petrophysics and reservoir simulation. This simulation workflow started with a petrophysical interpretation together with well surveys which serve as essential input data to build a single well predictive model. Rock typing using Heterogenous Rock Analysis (HRA) method resulted in a more detailed properties population along the vertical direction in tartan grid. Defining completions of the well and followed by conversion of tartan grid to radial grid was performed to accurately capture the pressure transient response near wellbore. The radial grid model was setup as a DTT model to forecast the pressure transient behavior of the reservoir incorporating the technology of a new intelligent wireline formation testing platform in the simulation inputs. The outcome of this study produced multiple scenarios incorporating different reservoir tightness from low to high with known thickness. The reason is that as the formation gets tighter; it is more challenging to achieve radial flow and predict producibility. By having uncertainty study in place, we can understand the outcome of each scenario then provide quantitative data to make decision on DTT feasibility, inlet and flow manager selections based on simulation result. This methodology not only optimizes the operation planning and execution, but also estimates pressure drop and the time needed to be on stationary for operational risk mitigation, which are in place to help operators improve certainty in decision making. The case study showed that the advanced 3D radial grid predictive model method addressed the advantage of Interval Pressure Transient Testing (IPTT) and DTT in accessing and evaluating reservoir connectivity, heterogeneity, and drainage radius. In this paper, we are the pioneer in this robust Intelligent FT integrated workflow globally, which was successfully implemented together with all wireline operations within planned time frame involved and delivered with exceptional results.

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