Unravelling the Mystery of Double Complex Unconventional Reservoirs on Tibetan Plateau by Highly Integrated Geophysical and Geological Modelling

Abstract

The study area belongs to Qaidam Basin of Tibetan Plateau. It has extremely complex structural and sedimentological conditions which seriously hinder in-depth geological understanding and effective exploration and development activities. We solve the problems to a great extent with highly integrated unique geophysical and geological modeling. The solutions mainly included: (1) Continuously improving the quality of seismic image by updating the PSDM cube twice during project execution based on a unique workflow of Coupled Geophysical & Geological Modeling; (2) Adjusting/consolidating seismic structural interpretation, well tops, and structural information on microresistivity images reiteratively to obtain robust structural interpretations; (3) Structural modeling with the method suitable for complex structural background; (4) Property modeling with combined constraints of well data, seismic trend, sedimentary cycle, variogram and geological understanding, such as using element logging interpretation results for Lithofacies, Mineral composition and Porosity models; (5) DFN fracture modeling with fracture statistics from microresistivity images, seismic edge-detection cube, seismic drivers and NFP geomechanical drivers. Not only are the double complex reservoirs effectively characterized, but also many meaningful geological conclusions are reached which in turn could guide more effective E&P activities, including (1) distributions of oil-bearing belts, pools, and high-production wells are all controlled obviously by structural patterns; (2) although the reservoirs belong to a very large lacustrine basin sedimentologically, great heterogeneity still commonly exists, with many local structural highs and lows causing quick variation of microfacies in plan view; (3) source rocks, reservoirs, traps and preservation condition are the key factors for oil abundance; (4) four geological conditions need to be carefully evaluated for any outskirt well design & drilling, etc. Based on the results, measured OOIP of tens of millions of tons has been summitted to the country, a bunch of kiloton-oil exploration wells have been drilled and dozens of optimized development wells have been placed in recent years. We realize "for the first time" in some aspects for effectively characterizing the saline lacustrine thin tight oil reservoirs on tectonically complex Tibetan plateau. This study can be referred to by other geologically complex regions in the industry.