The paper highlights the application of multi-component induction logging and formation pressure testing & sampling for determining oil column in a deep-water Pliocene turbidite formation composed of thin sand interbedded with shale. In such cases, conventional petrophysics using horizontal resistivity and bulk porosity will lead to an underestimation of the reserves or, at times, completely miss a potential hydrocarbon bearing zone. Presence of SOBM and logging in an unconsolidated formation makes fluid identification challenging.
Conventional bulk volume analysis, in contrast, gives a very pessimistic estimate at the pay interval compared to Laminated Sand Shale Analysis (LSSA). Carrying out formation pressure test and sampling based on these results helped in determining GOC from fluid identification tests and pressure gradient analysis, and clean formation oil samples were collected. Thereby, successfully meeting objective in a challenging unconsolidated environment by the integrated value added services
Krishna Godavari (KG) basin which is situated in Eastern Coast of India, was undergone by vast exploration activity since 1965. The KG basin comprises thick pile of sediments from Permian-to-Recent age and emerging as one of India's most promising petroliferous basin. Commercial accumulation of hydrocarbons occurs in sediments from the Permian to as young as the Pliocene. Offshore water channel over bank system has a lot of uncertainties, due to presence of thin beds, primarily, sand, silt and shale or their combination in term of their petro-physical properties and lateral extent. Complex geology of study area and inadequate reservoir characterization can cause significant amounts of hydrocarbons to remain un-recovered or to be recovered partially. Hence, proper evaluation of petro-physical parameters play an important role in the field development.
To mitigate the uncertainties of petro-physical evaluation for volumetric analysis, a clear understanding of formation resistivity anisotropy is required. . Multi-component induction tool measures vertical and horizontal resistivity (Rv and Rh, respectively) from multi frequency conductivity measurements while simultaneously solving for formation dip & azimuth at any well deviation. Measuring at multiple depths of investigation in three dimensions ensures that the derived resistivity are true 3D measurements that are unbiased by the low-resistivity effects of heterogeneous formations. The resulting estimated hydrocarbon and water saturations accurately represent the actual fluid contents, especially for laminated and anisotropic formations. In homogenous formations both resistivity (Rv & Rh) responses are similar, however, decrease in horizontal-resistivity compared to vertical-resistivity indicates resistivity anisotropy, which is because of thin bed formation in our study area. Basic logs are not able to capture actual porosity and resistivity of thin beds because of resolution. Based on the petrophysical analysis, potential hydrocarbon zones were identified and formation tester was used against these zones. Pretest showed high mobility and pumping was initiated on sand bed. Formation oil was identified and samples were collected. On confirming presence of oil, testing was carried out to estimate productivity.
