The Jobo Steamflood Project: Evaluation of Results (includes associated paper 17636 )

Abstract

Summary. This paper presents a description and a preliminary evaluation ofthe Jobo steamflood project, located in eastern Venezuela, from startup inMarch 1981 through Dec. 1986. The Jobo project consists of a steamdrive atoriginal reservoir pressure conditions (1,300 psia [8–96 MPa]) because anactive aquifer supporting this reservoir prevents pressure depletion byprimary steam-stimulated production. The primary recovery estimated forthis 8.5deg. API [1.01-g/cm3] accumulation of 10% stock-tank original oil inplace (OOIP) is expected to increase to above 45% by steamflooding. Todate, 36.2% of the project's stock-tank OOIP has been produced. and steam breakthrough is expected to occur during 1988. Production and injection well completions, as well as surface equipment, were evaluated for the future commercial development of this and other extra-heavy reservoirs in Venezuela. Introduction The largest extra-heavy (8.5 deg. API [1.01-g/cm3]) oilaccumulations in the world are located in eastern Venezuela, just north of the Orinoco River in the Orinoco oil beltand neighboring reservoirs. Although the Orinoco oil beltalone has 1.2 × 10(12) bbl [190 × 10(9) m3] of oil in place, only an estimated 10% will be recovered by primarysteam-stimulated production. After several secondaryrecovery methods were analyzed, steamflooding was selected as the most effective in these reservoirs, and theJobo pilot project was designed and implemented on thebasis of a numerical simulation study. The project wascarried out in the Jobo field to make use of existing infrastructures and because reservoir and fluidscharacteristics are essentially identical to thoseprevailing in the extra-heavy oil accumulations of the Orinoco belt. Project Description Project Objectives. The Jobo project was conceived toobtain information for future commercial developmentplanning of this particular reservoir and to obtaininformation about the vast amounts of extra-heavy, nonconventional oil from the Orinoco oil belt. The mainobjectives to be accomplished are listed here.1. To determine the recovery factor. The project willbe kept at constant pressure to prevent fluid movementinto or out of the system.2. Evaluate the technical and economic feasibility ofsteamdrive at original reservoir pressure conditions. Astrong natural water drive present in the reservoirprevents pressure depletion by primary steam-stimulatedproduction, which is the routine production method.3. To evaluate surface facilities and produced-fluidstreating and handling.4. To determine optimum production and injection wellcompletions.5. To calibrate numerical simulators for best predictionsand comparison of exploitation alternatives. To ensure the acquisition of the required data and thusto evaluate the project properly, a very comprehensivetest and measurements program was designed andimplemented during each phase of the project. Furthermore, a computer(surveillance) program was developed thatperforms material and energy balances on all streams thatenter or exit the plant and that validates measured production to calculate a field factor. Location. The Jobo project is located in the Jobo field, south of the state of Monagas in eastern Venezuela. Asseen in Fig. 1, the project is adjacent to the vastextraheavy oil accumulations of the Orinoco oil belt, whichspreads over an area of 21,000 sq miles [54 000 km2]through the states of Delta Amacuro, Monagas, Anzoategui, and Guarico, just north of the Orinoco River. Geology. The Jobo field reservoirs belong to the Oficinaformation, which is divided into the Pilon, Jobo, Yabo, and Morichal members, as shown in the stratigraphicsection of Fig. 2. The project is in Sand C of the Morichalmember. The sand's quality and thickness make it the bestobjective sand. These sands were deposited during theLower to Middle Miocene Age in a transgressive/regressive, shallow marine to fluvio-deltaic environment. Thegeneral structure corresponds to a monocline orientedeast/west and gently dipping (3 deg. [0.05 rad]) north. Anupstructure location was selected primarily to minimizewater encroachment from an active aquifer in the reservoir. Also, best-quality sands (clean and horizontallycontinuous)and fewer well completions (relatively virginzone) are characteristics of this zone: therefore, resultsof the project will not be affected by external influencesor heterogeneities and should be easier to interpret. These sands are composed mainly of quartz with onlyabout 7% clays, kaolinite being the predominant claymineral with only traces of illite and smectite. Althoughkaolinite belongs to the group of clays that do not swellby water absorption. JPT P. 1261^