Article pubs.acs.org/EF
Performances of Different Recovery Methods for Orinoco Belt Heavy Oil after Solution Gas Drive Teng Lu,† Zhaomin Li,*,† Songyan Li,† Binfei Li,† and Shangqi Liu‡ †
College of Petroleum Engineering, China University of Petroleum, Qingdao 266580, China RIDED, PetroChina, Beijing 100083, China
‡
ABSTRACT: Although foamy oil can improve the performance of solution gas drive in heavy oil, only about 5−15% original oil in place (OOIP) can be recovered under primary production. In this study, a series of micromodel flood experiments and sandpack flood tests were performed to evaluate the performances of water flooding, surfactant flooding, gas flooding, and foam flooding for enhancing the recovery of Orinoco Belt heavy oil after solution gas drive. Water flooding tests show that the sweep efficiency of water flooding was low as a result of the adverse mobility ratio caused by gas bubbles dispersed in the oil; about 10.57% OOIP was obtained in the sandpack study. Surfactant flooding tests indicate that the penetration of the surfactant solution into the heavy oil and the subsequent formation of gas bubbles and emulsified oil droplets in surfactant solution could reduce the mobility of water phase, thereby improving sweep efficiency, and oil recovery of 15.09% OOIP was recovered in the sandpack. Because of the viscous fingering, only 4.57% OOIP was obtained in the gas flooding test. The micromodel test of foam flooding shows that gas bubbles could reduce the mobility of the gas phase and the residual oil droplets could be pulled into oil threads by the viscoelasticity of gas bubbles, thereby reducing the residual oil saturation of foam flooding. The sandpack flood result shows that the oil recovery of foam flooding can reach 23.92% OOIP. sive.11,12 To improve the heavy oil recovery, a great deal of research has been performed on chemical flooding in recent years, including alkaline flooding, surfactant flooding, foam flooding, etc. The main mechanism of alkaline flooding and surfactant flooding in improving heavy oil recovery is the formation of an emulsion. Such formed emulsions either plug pore throats, leading to improved sweep efficiency, or are entrained along with the flowing aqueous phase.13−16 Foam can improve oil recovery by reducing gas mobility and redirecting gas flow, thereby increasing sweep efficiency in gasinjection.17,18 However, the results obtained so far are mainly focused on the heavy oil without solution gas. On the basis of a micromodel test, we found that plenty of gas bubbles were dispersed in the heavy oil after solution gas drive, which can influence the flow behaviors of the subsequent recovery methods. Therefore, the performances of the subsequent recovery methods for heavy oil reservoir after solution gas drive are not well understood. This study presents results of a laboratory investigation, including sandpack flood experiments and micromodel flood studies, for assessing the performances of water flooding, surfactant flooding, gas flooding, and foam flooding for enhanced heavy oil recovery after solution gas drive.
1. INTRODUCTION As the world faces declining production from conventional reservoirs and an ever-increasing demand for energy, development of unconventional oil reservoir, especially heavy oil, becomes critical in the petroleum industry. There are abundant heavy oil resources in the world, which are estimated between 6.04 × 1011 m3 and 9.86 × 1011 m3 in total.1,2 More than one trillion barrels of heavy oil in place are located in Canada, Venezuela, and Russia. The Orinoco belt in Venezuela is the richest heavy oil deposit in the world with an estimated 500 billion barrels of recoverable heavy oil.3 Some of the heavy oil reservoirs in Canada and Venezuela show anomalous behavior under solution gas drive. When the reservoir pressure is lower than bubblepoint pressure, the producing gas−oil ratio does not increase rapidly, and the pressure drop rate is slow. Similar behavior is being reported in other heavy oil reservoirs in China and Albania.4,5 Several theories were proposed to explain the anomalously high primary recovery under solution gas drive. Most researchers agree that foamy oil is the main mechanism of the solution gas drive process of heavy oil.6,7 In foamy oil, gas is highly dispersed in the oil in the form of small gas bubbles.8,9 However, though foamy oil can improve the performance of solution gas drive in heavy oil, only about 5−15% of the original oil in place (OOIP) can be recovered under solution gas drive.10 Therefore, there is still a large amount of remaining oil after the solution gas drive, and it is important to research the subsequent recovery methods. Water flooding is a common and inexpensive secondary oil recovery technique for the heavy oil reservoir. However, the incremental recoveries by water flooding are quite low for high viscosity heavy oil, but in many heavy oil fields, water flooding is still commonly applied because it is relatively inexpen© XXXX American Chemical Society
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2. EXPERIMENTAL SECTION
2.1. Fluids and Chemicals. Crude oil was collected from the MPE3 block in Orinoco Belt, with a dead oil viscosity of 12 041 mPa·s at a reservoir temperature of 54 °C. Four components of the heavy oil were tested, using column chromatography, as shown in Table 1. Gas used in this study consists of CH4 and CO2 (provided by Tianyuan
Received: December 9, 2012
A
dx.doi.org/10.1021/ef400511s | Energy Fuels XXXX, XXX, XXX−XXX
Energy & Fuels
Article
Inc., China, with a purity of 99.99%), and mole fractions are 87 and 13%, respectively.
Table 1. Four Components of the Heavy Oil saturation fraction (wt %)
aromatic fraction (wt %)
colloid fraction (wt %)
asphaltene fraction (wt %)
22.25
42.51
21.73
13.51
The bubblepoint pressure of the live oil was 6.0 MPa, and the solution gas oil ration (GOR) was 18m3/m3. The surfactant agent used in this study was HY-2 (provided by Shengli oilfield, China, with a purity of 33.5%). The surfactant solution with the concentration of 0.5 wt % was fully stirred by the magnetic stirring apparatus (Jintan Inc., China) for 2 h. 2.2. Apparatus. The apparatus used in this study is shown in Figure 1. An ISCO pump (model 100 DX, with flow accuracy
