Multilateral-Horizontal Wells Increase Rate and Lower Cost Per Barrel in the Zuata Field, Faja, Venezuela

Abstract

Abstract Petrozuata, C.A is a joint venture (JV) company between Conoco Orinoco Inc. and PDVSA. This JV is developing extra heavy crude in a 74,000-acre block in the Zuata field in the western portion of the Faja del Orinoco in Venezuela. After the initial single lateral wells were brought on production an opportunity was identified to change the development program to multilateral wells in order to increase production rates. The geometry of multilateral wells is designed to fit the actual sand distribution and depositional environment that ranges from subarial fluvial to marine tidal systems. The various forms of multilateral wells drilled by the JV include stacked dual lateral, stacked triple lateral, gullwing dual lateral, gullwing triple lateral or crow's foot, and pitchfork dual lateral wells. In addition a fishbone multilateral concept consisting of a "spine" or main lateral with liner connected to many ribs or fishbones without liners has been used in single lateral and multilateral configurations. The geologic and geographical reasons for drilling these different types of multilateral wells are reviewed. The result has been an increase in production rate per well that is nearly proportional to the effective lateral length connected to the well bore at a lower cost than possible with single lateral wells of the equivalent length. Introduction Petrozuata, C.A. is a joint venture company between Conoco Orinoco Inc. and PDVSA and is referred to as the Company or the Operator in this document. The Company is developing extra heavy crude in a 74,000-acre block in the Zuata field in the western portion of the Faja del Orinoco in Venezuela (Figure 1). Built from the ground up in less than three years, Petrozuata has drilled over 306 horizontal laterals for production and 137 vertical wells for information. Oil production has exceeded 100 MBOPD with plans to reach 120 MBOPD in 2001. It is the world's largest multilateral development. Each horizontal well is custom designed and geosteered to assure efficient reservoir access based 3D seismic, vertical stratigraphic well control and detailed geologic facies maps. In 1996 the Company finalized the basic development plan to primarily use single lateral horizontal wells under depletion drive with no thermal stimulation or other pressure support techniques to produce 120 MBOPD for 35 years. The project has an early production period prior to the 35 year plateau period to allow developing the 120 MBOPD production capacity while a delayed coking upgrader is constructed near Jose on the northern coast of Venezuela (Figure 2). The basic well layout in this plan is to center horizontal laterals of 1200 meters length within drainage rectangles 600 meters wide by 1600 meters long (Figures 3 & 4). Since the reservoir consists of multiple sand bodies that may be locally isolated but are generally interconnected on a field-wide scale, horizontal wells are placed vertically above each other as needed to develop the stacked sand bodies within local drainage rectangles. Generally Electric Submersible Pumps (ESPs) are used initially and Progressive Cavity Pumps (PCPs) are planned as well rates decline. Downhole and surface dilution with a light crude oil, or naphtha returned from the upgrader, is used to improve viscosity and dehydration. After shooting 3D seismic in 1996 and 1997, the Company started drilling in mid 1997. First oil production started August 1, 1998 and, with the drilling of additional wells during the early production phase, production ramped up to over 90 MBOPD by mid-year 2000. The project should enter the 120 MBOPD 35-year plateau in 2001 after the upgrader is fully functional.