Sweet-Spotting and Unlocking Tight Gas Volumes of Lower Miqrat Formation

Abstract

Abstract Miqrat is a complex clastic deep tight gas reservoir in the North of the Sultanate of Oman. The Lower unit of the Miqrat formation is feldspatic sand characterized by low permeability not exceeding 0.1 mD and porosity up to 12 %. Based on results of the appraisal campaign of Field X, it contains significant volume of gas. However the production test data after fraccing showed mixed results. The objective of this study was to explain the production behavior and identify the sweetspot area for further development. Understanding the reason of possible overestimation of log derived Hydrocarbon saturation is important. Thus the interpretation of conventional and special logs was revisited. In parallel, all the available core data including SCAL and thin sections were scrutinized. Besides, the analysis of hydraulic fracture propagation, well tests, cement quality, PLT including Spectral Noise Log was performed. The wells were subdivided into categories according to their production results:–wells producing no water–wells with water channeling from the water leg of Middle Miqrat–wells with transition zone intervals with 2 phase inflow of water and gas. Based on the integrated analysis, extend of the gas and transition zones was established, and the location of future wells optimized. From the Spectral Noise log and Temperature data, water crossflow/channeling from Middle Miqrat was identified in 2 wells, either because of broken thin sealing shale above Lower Miqrat or due to poor cement quality. The sweetspot area with commercial production was mapped. Substantial gas volumes have been unlocked. Besides, an explanation of the uncertainty in log derived saturation was suggested. Core plugs and thin sections revealed presence of partially filled vugs, which is not a typical case in a clastic environment. The origin of this porosity is puzzling and likely due to dissolution of early diagenetic nodules. The rock with poorly connected vugs has high resistivity even if it is water bearing. The review of capillary pressure data revealed that the transition zone could exceed 100 m. This finding is consistent with the interpretation from well tests. The most practical implication of the current study potential of Lower Miqrat is unlocked. The integration of Open hole and cased hole logs and the additive information from Spectral Noise log for channeling/crossflow identification is shown. Presence of vuggy-like porosity in clastic sections and the impact of isolated vugs on log derived Saturation is demonstrated.