Development Optimization of a Marginal Oil Field in Bohai Bay, China

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 16669, ’Development Optimization of a Marginal Oil Field in Bohai Bay, China - Integrated Solutions To Overcome Challenges in Offshore Horizontal-Well Construction,’ by Chaomin Nie, Yongsheng Zhao, Lv Tan, Yong Jia, and Gang Zhai, China National Offshore Oil Corporation Tianjin, and Parlindungan Monris Halomoan, Xu Chong Hui, Wang Yong, Wang Fei, and Dong Jianyi, Schlumberger, prepared for the 2013 International Petroleum Technology Conference, Beijing, 26-28.March. The paper has not been peer reviewed. Nine horizontal wells, including one injector well, were drilled in a marginal oil field in Bohai Bay, China. Seismic inversion indicates that sand properties and connectivity vary dramatically across the field. A multiple-aquifer system was apparent, and the gas/oil-contact (GOC) and oil/water-contact (OWC) levels were unknown. Furthermore, the only well control was from three vertical exploration wells and two directional offset wells. An advanced distance-to-boundary well-placement technique using azimuthal deep-directional electromagnetic logging-while- drilling (LWD) technology was applied to overcome these challenges and to enhance reservoir understanding. Introduction The BZ oil field is located in the southern part of Bohai Bay, approximately 160 km southeast of Tanggu, Tianjin (Fig. 1). It is a small oil-bearing area (9.km2) isolated by secondary faults generated at different geological periods and by stratigraphic depositional borders. Two other producing oil fields are located in the northern and western parts of the BZ area. Although the original oil in place (OOIP) of the oil field is estimated at only 1261.89×104 m3, this marginal oil field is expected to be profitable to develop and put into production by sharing the facilities of the other two oil fields. The BZ structure is part of the complex fault system on the northwest side of the Huanghekou depression on the west side of the Bonan uplift. Because of the oil field’s isolation, a multiple-aquifer system exists. A pilot study based on core and sequence-stratigraphy analysis of multiple wells shows that the reservoirs are distributary channel sands of a shallow lake delta plain. The channel sands have medium-to-high porosity and permeability. The seismic-data analysis suggests that the properties may vary laterally. Meanwhile, uncertainty in the top gas and bottom water levels adds to the complexity of this field. The GOC and OWC levels were unknown before this horizontal-well-drilling program. Horizontal-Well-Drilling Program Two platforms were designed to develop this complex oil field: BZ-A platform, to drill 11 wells, and BZ-B platform, to drill five wells. Among these 16 wells, 10 horizontal wells were designed as producer wells, five deviated wells were designed as injector wells for formation-pressure maintenance, and one deviated well was designed to supply water for the injector wells.