The Study Of Mechanism Of Cold Heavy-Oil Production With Limited Sand Influx In Blocks 6, Sudan

Targeting the abundant overseas heavy oil resources reserved in unconsolidated sandstone reservoirs, this paper has put forward an advanced with Sand (CHOPS) technology to economically and effectively develop Block 6 of Sudan. About 80% of the petroleum resources, lately discovered in Block 6, are heavy oil. To efficiently produce and utilize the heavy oil resources is an important measure to improve the efficiency of overseas oil and gas development. The advantages of CHOPS include simple completion, dramatic increase in productivity and low production cost.The Fula heavy oil reservoir of Block 6 in Sudan is buried deep and unconsolidated, having low pore pressure, high oil viscosity and low GOR. The CHOPS technology is applicable to the reservoir. This paper has conducted laboratory experiments of CHOPS under the simulated reservoir conditions, determined the critical erosion and matrix sand influx conditions for wormholes to form, and analyzed the critical pressure drop and erosion constant for wormholes to form.Based on the black oil model, this paper has established a mathematical model of fluid-structure interaction (FSI) for oil-water two-phase flow in deformed medium, by using percolation mechanics, elastic-plastic mechanics and rock-soil mechanics, built a linear elastic theoretical model of 2D stress distribution around the wellbore (open hole completion and perforation completion) and neighboring reservoirs, and solved the models by the finite element method. The results indicate that sand influx due to shear failure mainly happens within the range about 2-fold of the borehole radius, and the stress concentration zone formed in the perforation bottom is vulnerable to shear failure resulted sand influx. Besides the above work, this paper has also:a) analyzed the impacts of reservoir permeability, internal friction angle, cohesion, elastic modulus and Poisson's ratio on the critical pressure drop; b) researched the process of wormhole development around the perforated holes, with the critical plastic strain as the shear failure evidence based on the element birth-death model; c) performed dynamic prediction of the sand influx caused by CHOPS; d) optimized the completion plan for CHOPS in Block 6; e) thoroughly studied the impacts of sand control on the well productivity, the sand influx and the wormhole length when CHOPS is applied.CHOPS has already been successfully used in the Stage I development of the heavy oil reservoirs in Block 6, Sudan. All of the 20 wells applying CHOPS have increased the production dramatically—the average oil production per well has increased from 35m(?)/d to 85 m(?)/d, equivalent to an annual heavy oil production of 500,000 tons, up by 290,000 tons in the current year. In addition,83 wells have been drilled and completed for the Stage II development of the heavy oil reservoirs in Block 6, generating an annual productivity of 2,000,000 tons. As of June 2010, about 12% of the reserves have already been produced from the Fula-North heavy oil reservoir, but the production rate is still as high as 2.2%. Without question, the CHOPS technology has achieved very good effect.The major innovations of the paper lie in that it has conducted laboratory experiments of wormholes formed in cold heavy oil production with sand, researched the process of wormhole development around the perforated holes, with the critical plastic strain as the shear failure evidence based on the element birth-death model, completed numerical simulation of the sand influx process in CHOPS by using the finite element method, put forward a new concept of "controlling coarse sand and producing fine sand" and optimized the parameters of limited sand control.