Reservoir Modeling for Horizontal Exploitation of a Giant Heavy Oil Field - Challenges and Lessons Learned

Abstract

Abstract The Hamaca Field, located in Venezuela's Orinoco Heavy Oil Belt, is a giant extra-heavy oil accumulation operated by Ameriven, an operating agent company for PDVSA, Phillips and ChevronTexaco. Over the 35-year life of the field, more than one thousand horizontal laterals are planned in order to deliver 190,000 BOPD to a heavy-oil upgrader facility. Reservoir models are built to support a broad continuum of activities in order to meet this objective. This paper will review the Hamaca reservoir modeling process, the challenge of integrating many sources of geologic and geophysical constraints including horizontal well information, the focus on continuous model improvement, and issues unique to Hamaca rock and fluid properties. Background The Hamaca Field is located in Venezuela's Orinoco Heavy Oil Belt, which is reported to contain more than 1.2 trillion barrels of heavy and extra heavy oil in a huge stratigraphic trap on the southern flank of the Oriente Basin (Fig. 1). The Hamaca concession area, which covers 160,000 acres, contains 8–10 API gravity oil trapped in shallow fluvial-deltaic reservoirs of the Oficina Formation (Miocene age). Sandstone reservoirs of the Oficina Formation at Hamaca were generally deposited in a bed-load dominated, fluvial-deltaic environment. Reservoir properties are excellent with porosity values of up to 36% and permeability values of up to 30 darcies. Hamaca crude is considered "foamy" and is generally saturated with gas at reservoir conditions1. Over the 35-year life of the field, over 1000 horizontal laterals are planned in order to deliver 190,000 BOPD to a heavy-oil upgrader facility, which is currently under construction1. To date, more than 110 horizontal wells have been drilled to produce from the Hamaca reservoirs. Oil is being produced under "cold production" methods, (no added heat) using progressive cavity pumps to bring oil to the surface. Cold production is possible due to the extended length of the horizontal wells (5000'), excellent reservoir properties and the "foamy oil" nature of Hamaca crude2. The heavy oil will be mixed with diluent just downstream of the wellheads to facilitate transport to the upgrader facility. The Hamaca crude will be converted to a sweeter crude product of approximately 26° API at the upgrader. The combined use of both well and seismic data is critically important for characterizing the stratigraphic complexity of the Hamaca fluvial-deltaic systems. To assist in targeting sweet spots for horizontal well placement, a 250 km2 3-D seismic survey was acquired along with the drilling of 91 stratigraphic information wells with an average separation distance of about 1.5 km.