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This paper presents a methodology for the probabilistic analysis of an infill or step-out opportunity using numerical simulation. Sensitivity and uncertainty analyses for all involved parameters were evaluated through different experimental design techniques. Subsequently, a proxy model was established to reproduce the numerical model performance. Finally, three appropriate solutions were selected from a large population of realizations corresponding to probabilistic percentiles (90%, 50%, and 10% certainty that the specified volume will be recovered). This proposed methodology helped the asset team to evaluate the well candidates more precisely, confidently, and in less time than the current standard methodology. More knowledge about the variables and their effects on overall outcomes was also gained, which helped the team make more-informed decisions. The workflow used the same numerical modeling software, incorporating and facilitating the changes of both static and dynamic properties simultaneously. A case study from Teak field, on the east coast of Trinidad, illustrates the applicability of the methodology and compares its results to those obtained using the standard workflow for the asset. The methodology is one of the latest developments in reservoir simulation, and it has not yet been incorporated into the operator's common practices and procedures for exploitation of the TSP fields.

In an offshore mature asset workover jobs involve high cost and operational risk that impact on the profitability of the projects. Non-rig interventions are a more sustainable approach to effectively sustain production. The fact that some reservoirs are depleted while many are water flushed often result in modest incremental gains. Due to the age of the asset, several wells present mechanical issues which make any intervention more challenging. The non-rig methodology has proven to be well-suited to these conditions. This paper will describe the criteria and technology used to mitigate the production decline of the TSP (Teak, Samaan & Poui) asset located off the south-east coast of Trinidad. TSP is a mature oil field which has been producing for almost 40 years. The main constraints for flow assurance are sand production, scale and paraffin deposition, high IGLR, skin damage, high water cut, depleted reservoir and mechanical problems. A variety of non-rig interventions have been employed since 2006 in order to mitigate the mentioned constraints and therefore maximize production from the field. These interventions include tubing and formation acid/de-wax jobs, gas lift valve changeout, addition of new perforations, tubing punch, sand clean out, thru-tubing gravel pack and other jobs aimed to acquire information such as pressure surveys and cement, production, reservoir saturation and multi finger logs. These jobs, together with regular gas lift optimization exercises and re-activation of previously shut-in wells, have proven to be quite effective at slowing the natural production decline. An annual technical and operational screening of all wells (active and shut-in) is performed and the under-performing wells are identified and targeted for the non-rig campaign and reactivation. In addition to that, multi-rate tests are carried out throughout the field prioritizing those critical wells. This ensures that the injection gas rates are at their optimal values, maximizing the oil rates and saving injection gas volumes. The non-rig, well re-activation and GLO campaigns have maintained the annual production decline of the TSP field between 8 to 12% while facing operational and reservoir issues inherent in an aging field.

In 2005, NGC, Petrotrin and Repsol E&P T&T Ltd. as joint venture partners, acquired the TSP asset with Repsol as the operator. The three fields, Teak, Samaan and Poui, have been in production for over 40 years and are highly complex, extremely compartmentalized and consist of over 10 different sands and reservoirs. Over 100 PVT files for the three fields are available; most of which were done in the 1970's by different labs using different protocols and procedures. All files were handed over in paper form which needed digitization as well as validation. Valid PVT data provides vital information for the characterization of reservoir fluids. The establishment of fluids' physical and PVT properties help determine in situ and stock tank volumes, strategies for production, flow assurance issues for facilities design and provides guidelines for effective and efficient reservoir management throughout the life of the asset. Numerous techniques exist for assessing and evaluating the quality of PVT data. This paper will describe the best practices used to validate TSP PVT data, such as the material balance tests and the Y-function linearity tests as well as the applications of the validated data through examples and case studies. Some of which include the development of trends which can be extrapolated for use in new prospects, infill and developmental drilling. Additional benefits include the recognition of flow assurance issues such as wax and sulphur compounds and the sampling and design of relevant PVT experiments for new wells. Production history combined with valid PVT data provides a powerful tool to help in the prediction of expected fluid types and fluid behaviour as pressure changes in planned new wells. It also provides additional technical support for which improvements to the fluid sampling program can be made to acquire the most representative fluid samples from the reservoir.