Jia, Ying (Petroleum Exploration and Production Research Institute, SINOPEC) | Shi, Yunqing (Petroleum Exploration and Production Research Institute, SINOPEC) | Huang, Lei (Research Institute of Petroleum Exploration and Development, Petrochina) | Yan, Jin (Petroleum Exploration and Production Research Institute, SINOPEC) | Sun, Lei (SouthWest Petroleum University)
The YKL condensate gas reservoir is one of the biggest condensate gas reservoirs in China and has been developed more than 10years. At present, the combination of subdivision layer, production speed optimization and horizontal well drilling has been the key to economically unlocking the vast reserves of the YKL condensate gas. The primary recovery factor, however, remains rather low due to high capillary trapping and water invasion. While primary depletion could result in low gas recovery, CO2 flooding provides a promising option for increasing the recovery factor.
The objective of this work is to verify and evaluate the effect supercritical CO2 on enhancing gas recovery and analyze the feasibility of CO2 enhance gas recovery (CO2 EGR) of condensate gas reservoir.
Firstly, novel phase behavior experimental procedures and phase equilibrium evaluation methodology for gas-condensate phase system mixed with supercritical CO2 with high temperature were presented. A unique phase behavior phenomena was also reported. Then, CO2 floodingmechanism in condensate gas reservoir was analyzed and clarified based on experiments. Finally, a series of numerical simulation work were conducted as an effective and economical means to maximize natural gas recovery with the lowest CO2 breakthrough by varying strategies, including CO2 injection rate, injection composition, andinjection timing. Meanwhile the CO2 storage volumes of different strategies were calculated.
The results show that higher gas recovery factor can be achieved with CO2 injection through appearing interphase between two fluids, maintaining reservoir pressure, driving gas like "cushion" and controlling water invasion. All strategies have moderate to significant effects on gas production. The control of injection and production ratio needs to be balanced between pressure transient and CO2 breakthrough over the producer to obtain the maximum gas production. The varying injection pressure shows a positive effect of enhancing gas production. Numerical simulation indicated that the recovery of gas reservoir was improved by around 10 percent. The total CO2 storage would be around 30-40% HCPV.
The research showed that CO2 flooding presents a technically promising method for recovering the vast condensate gas while extensively reducing greenhouse gas emissions.
Jiawei, Kao (China University of Petroleum) | Yan, Jin (China University of Petroleum) | Yunhu, Lu (China University of Petroleum) | Bing, Hou (China University of Petroleum) | Jinlong, Du (China University of Petroleum) | Huijie, Zhang (China University of Petroleum)
ABSTRACT: Cement sheath integrity supports the long-term safety production of oil and gas well. In order to research failure mechanism of cement sheath in HPHT conditions, uniaxial and triaxial compressive tests and cyclic loading test of cement are conducted, and mechanical property and failure characteristics of cement are analyzed by using statistics damage mechanics. A simple formation model and an interbedded one are built in FLAC 3D Software to analyze the damage characteristic and the influence factors of cement, and numerical results show that: with the increase of wellbore pressure, elasticity modulus of formation and cement, and non-uniformity coefficient of ground stress, the damage of cement will increase; During cyclic loading and unloading, damage of cement will increase with cycle time, but most of the damage will occur in the first cycle; The reduce of pore pressure will aggravate the damage, especially in the border between different formations. Damage mechanics can give a better way to evaluate cement sheath integrity in the life of a well.
Cement sheath integrity provides long-term safety production for oil and gas well. If the integrity of the wellbore is not sustained completely, it could result in wellhead pressure conditions, increased cost and environmental issues, even engineering abandoned.
In the past years, some achievements focused on cement sheath integrity have been published. Bourgoyne et al. (1999) take Portland cement as a brittle material, and it trends to crake when tensile loads induced by thermal and stress exceed tensile strength . A Modified Cam-Clay Model based on poro-mechanics is built by Thiercelin et al. (1998) to analyze the shrink behavior of cement . SRC (System Response Curve) Method (2005) raised by Method D. Fourmaintraux et al. can predict the failure of cement . Siavash Ghabezloo et al. (2008) provide a porous medium framework to analyze the influence of porous media parameters and pore pressure . Iverson et al. (2008) study the mechanical property of different kinds of cement in HTHP conditions . Based on the previous studies, Axel-Pierre Bois et al. (2012) use a mechanistic model which consider cement as an inhomogeneous porous material to forecast cement-sheath integrity . Arash Shadravan et al. (2014 and 2015) study the fatigue failure of cement under circle loading [7,8]. Torbj⊘rn Vrâlstad et al. (2015) study the failure of cement under thermal cycle .
Xueqing, Teng (Tarim Oilfield, PetroChina) | Pei, Yang (Tarim Oilfield, PetroChina) | Ning, Li (Tarim Oilfield, PetroChina) | Chengxin, Yang (Tarim Oilfield, PetroChina) | Yan, Jin (China University of Petroleum(Beijing)) | Yunhu, Yunhu (China University of Petroleum(Beijing)) | Bo, Zhou (Tarim Oilfield, PetroChina) | Xiaoliang, Wang (Tarim Oilfield, PetroChina) | Feng, Zhang (Tarim Oilfield, PetroChina) | Tao, Zhang (Tarim Oilfield, PetroChina) | Xiaohong, Zhou (Tarim Oilfield, PetroChina)
In Tarim Oilfield the Ordovician carbonate reservoirs develop lots of cracks and caves. The formation pressure is very low(>6000m,less than65MPa), leading to the narrow mud weight window(MWW) problem. Serious lost circulation and reservoir damaged was encountered when we use the traditional overbalanced drilling. There’s no report of the whole process underbalanced drilling technique (including the underbalanced drilling, underbalanced tripping, underbalanced logging and underbalanced completions, etc.) being used in such formations in China. Based on the analysis of difficulties encountered by traditional overbalanced drilling methods such as serious lost circulation , horizontal wells cannot reach the design sections, serious damage to the reservoir, the feasibility analysis and construction plan of the whole process underbalanced drilling in Y block is p roposed. The first whole process underbalanced drilling of horizontal wells in Tarim Oilfield was conducted and completed. Finally 6 layers of reservoirs are being discovered, the cumulative thickness is 16m, which increases the rate of oil and gas discoveries. Compared with the on-site well , the efficiency of drilling is greatly improved, no lost circulation and no complex situation encountered ; the ROP increases 74% compared to the adjacent wells in the same layers. It also created the deepest drilling depth record using the inflatable mud in China which shows great effect in improving ROP and protecting reservoir.