Shell applies modern decline analysis and material balance to answer the question.
Hector Gomez Alonso, Majida Al-Kharusi, Phyllis Yeo Niam Chay and Mike German, Sarawak Shell Berhad
This article presents the results from using modern decline analysis and material balance in a mature field in Sabah State, Malaysia. It represents the first part of ongoing subsurface evaluations. Identification of non-drained areas of the reservoir using modern decline analysis, together with the use of material balance, successfully allowed evaluation of the production potential and the determination of the viability of infill well locations.
Prior to obtaining a clear understanding of the subsurface drive mechanisms and production data, reservoir simulation was used to establish reservoir potential and carry out infill drilling evaluations. The results were highly variable and encouraging in some cases, and somewhat disappointing in others. Subsequent well results indicated large discrepancies between the static models and the actual field results. Once these discrepancies had been reconciled, a consistent understanding of reservoir performance began to develop.
This article also presents the results of applying modern decline analysis and material balance techniques to different reservoirs, starting from the basic steps of quality assurance and quality review of the entire production data, in order to incorporate them together with the pressure of the neighboring wells to the future infill target. Each reservoir was matched to the observed pressure, for both modern decline analysis and material balance, which again showed signs of non-drained areas, secondary support mechanisms and infill opportunities. Modern decline analysis was carried out for each well and, from the results, a map of contacted oil volume and a recovery factor was generated for each reservoir. Later, material balance was applied to assess the energy levels of the non-drained areas. As a result, several optimization and infill opportunities were identified.
Nowadays, one of the main challenges is to find new opportunities in mature fields. This methodology can be considered as a first step toward the use of a full-field 3D model to realize opportunities. The proposed methodology is simple and easy to use. This case study clearly demonstrates that subsurface success depends more on correct reservoir understanding rather than the degree of complexity with which it is modeled. This method gave us not only a good understanding of the reservoir in terms of production and pressure, but also in terms of geology, which brought out aspects that were not identified in the past and that played an important role in managing production from new wells.
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This article was adapted from a professional society paper for which World Oil was granted the right to print one time only. Therefore, to review the article, you should refer to the actual World Oil magazine in which it originally appeared.
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