Application of Unconformity Identification and Evaluation in the Optimizing of Offshore Oilfield Development Plan: A Case Study of CFD Oilfield in Bohai Bay Basin

Abstract

CFD is a buried hill drape anticline in Bohai Bay Basin. In the early stage of oilfield development, production wells are designed at each structure high by overall development plan (ODP) in order to develop the reserves near the top of Ed formation. During the development, it exposes that some of the structure highs do not get any hydrocarbon accumulation. This problem makes our ODP less effective and causes considerable waste of investment. To solve the problem, we take a series of work to analyze the main controlling factors of hydrocarbon accumulation at structure highs, reevaluate the risk of wells that have not been implemented, search potential reserves and optimize the ODP. We apply genetic inversion to describe the reservoirs and then identify the two unconformities at the top and base of Ed formation. The sealing ability of unconformities typically depends on the lithology on the two sides. Since the top of Ed formation is a truncated unconformity covered by massive sandstone, the unconformity has poor sealing ability. It means once the cap rock at the top of Ed was eroded, the structure high will not get hydrocarbon accumulation. Meanwhile the base of Ed formation is an overlap unconformity covering the dense granite buried hill, thus the unconformity should have good sealing ability. That means sand bodies overlap on the side of buried hill near the base of Ed formation could be effective traps. Base on this perspective, we build unconformities, structure highs, sand bodies in 3D geological model and describe the spatial composing relations of them to evaluate the possibilities of hydrocarbon accumulation in different positions. After analyzing risk of structure highs and potential of sand bodies, we optimize the ODP and gradually move the well positions which were located in the structure highs with great risk to the sand bodies with great potential near the base of Ed formation. The results show that our predictions on hydrocarbon accumulations in the structure highs are accurate; three wells get geological reserves over 400×104t near the base of Ed formation with high productivity. In the context of the current low oil price, our study optimizes ODP by analyzing effects of different unconformities on hydrocarbon accumulation, effectively avoids waste and increases the return of investment while increasing reserves and production. Moreover it provides new ideas for the exploration of similar structures and development of similar oilfields.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017