Rui, Gao (Research Institute of Petroleum E&D-LangFang, CNPC) | Xin, Wang (Research Institute of Petroleum E&D-LangFang, CNPC) | Mingguang, Che (Research Institute of Petroleum E&D-LangFang, CNPC) | Bo, Cai (Research Institute of Petroleum E&D-LangFang, CNPC) | Chunming, He (Research Institute of Petroleum E&D-LangFang, CNPC)
As permeability of tight oil reservoir is generally less than 0.1md, diameters of pore throats are primarily at the micrometer- and nanometer-scale. Different from conventional reservoir, the percolation occurs mainly as non-linear flows so that the threshold pressure has a significant effect on the flow of fluids within the reservoirs. In this paper, a fracture optimization method for SRV Fracturing of tight oil reservoirs that considers threshold pressure introduced. Through numerical simulation, the fracture parameters of the tight oil in the Mahu reservoir in western China is optimized.
Based on the experimental results of constant-rate mercury injection experiment on cores collected from Mahu reservoirs in Xinjiang oilfield, the relationship between the core and the threshold pressure at different permeability was obtained. Later, a mathematical model of reservoir and fractures was created based on the characteristics of tight oil reservoir and of percolation through artificial fractures. By using the CMG simulator, three level of permeability, 10md, 1md, and 0.1md, were applied to the model separately with the corresponding threshold pressure gradients were 0.01MPa/m, 0.1MPa/m, and 1.0 MPa/m, respectively. Then the model's oil productions were estimated in two cases: when the threshold pressure was considered and not considered, to examine the influence of threshold pressure on oil production. Further research was then carried out to explore proper SRV fracturing methods for reservoirs with different physical properties.
The constant-rate mercury injection experimental results show that when the core permeability is less than 0.1md, the threshold pressure gradient is 3.11 times larger of the core with 1.0md permeability, and 9.65 times larger of the core with 10md permeability. The influence of threshold pressure on oil production should be considered during the numerical simulation of the fracturing of the tight oil reservoir. Compared with the numerical simulation results without considering the threshold pressure, the optimization of artificial fracture parameters with same production are quite different by considering the starting pressure. The cumulative production of 1 year reduced 84.77% when the threshold pressure gradient is about 0.14MPa/m, with the length of the horizontal section is 400m and the permeability is 0.1md, and also under the same crack length, spacing and diversion capacity. Considering the threshold pressure gradient, it is necessary to shorten the intervals between fractures and reduce the flow distance of tight oil from matrix to fractures, so as to increase the production and thereby increasing matrix's contribution to production capacity.
The threshold pressure gradient has a great influence on optimization results of multistage fracturing in tight oil reservoir. The results of paper are applied to the development of Ma-18 well block in Mahu tight oil reservoir. The research findings and methods provide guidance for multistage fracturing optimization in similar tight oil reservoirs.
Xin, Wang (Key Laboratory of Reservoir Stimulation, Fracturing and Acidification Technology Service center, PetroChina Research Institute of Petroleum E&D) | Yunhong, Ding (Key Laboratory of Reservoir Stimulation, Fracturing and Acidification Technology Service center, PetroChina Research Institute of Petroleum E&D) | Nailing, Xiu (Key Laboratory of Reservoir Stimulation, Fracturing and Acidification Technology Service center, PetroChina Research Institute of Petroleum E&D) | Zhen, Wang (Key Laboratory of Reservoir Stimulation, Fracturing and Acidification Technology Service center, PetroChina Research Institute of Petroleum E&D) | Fang, Wang (PetroChina Coalbed Methane Company Limited) | Haibing, Lu (Key Laboratory of Reservoir Stimulation, Fracturing and Acidification Technology Service center, PetroChina Research Institute of Petroleum E&D) | Gaochuan, Huang (Key Laboratory of Reservoir Stimulation, Fracturing and Acidification Technology Service center, PetroChina Research Institute of Petroleum E&D)
A large number of natural gas resources of medium-high rank coal reservoirs has been achieved in Qinshui basin and other areas in China, which presents broad prospect of exploitation. Nevertheless, this low-porosity (3%-5%), low-permeability (0.01mD-3mD) type of reservoirs require hydraulic fracturing to realize commercial development. As relatively long period of drainage and regional depressurization are needed before the initiation of coalbed methane (CBM) production, the fractures firstly offer channels for drainage. Meanwhile, it is easy for the soft coal and proppants to be embeded. Therefore, long fractures and high conductivity through fracturing treatments are needed to gain better production performance. Thus, the key factors to get optimal effectiveness of well completion are to accurately acquire understanding of the hydraulic fractures expanding and supporting conditions.
This paper introduces a joint fracture-diagnostic technology of microseismic mapping and microdeformation measurements to monitor nine wells of two cluster well platforms of CBM reservoir. The pattern, orientation and size of fractures are obtained from microdeformation measurements, and the scope of stimulation is obtained from microseismic mapping.
Some conclusions from the studies are as follows: (1) it is hard for the fractures in coal seam to propagate, and their lengths usually range from 44 m to 119 m. The fracture length estimated from microdeformation measurements is smaller than the results from microseismic mapping. (2) A new method to estimate stimulated reservoir volume based on microdeformation measurements through calculating volume envelope is set up. The SRV estimated from microdeformation measurements is much less than the one from microseismic mapping. As the CBM reservoir has a high leak-off coefficient, the SRV estimated from microdeformation measurements is closer to the reservoir volume controlled by the effective propping fractures. (3) On the same platform, the orientation of fractures in the latter constructed well changes due to the stress interference from the former constructed well, and the orientation variation of fractures in the last constructed well is the biggest.
These understandings are of important influences on CBM fracturing design and construction, which can be used to determine reasonable stimulation volume, reasonable construction sequence and interval of platform wells based on the real fracture propagation characteristics, and finally to obtain the optimal well performance.
Yuning, Wang (School of Geoscience and Technology, Southwest Petroleum University) | Xin, Wang (Production Engineering and Research Institute of Daqing Oilfield Company Ltd) | Meng, Cai (Production Engineering and Research Institute of Daqing Oilfield Company Ltd) | Renyong, Liu (Production Engineering and Research Institute of Daqing Oilfield Company Ltd) | Qingfeng, Yue (Production Engineering and Research Institute of Daqing Oilfield Company Ltd) | Qinghai, Yang (RIPED, PetroChina)
In high water cut oilfield, the separate-layer producers often face the problems of low separate-layer control level, difficult water locating and plugging, high operation cost and low testing and adjusting efficiency. As to solve these problems, new separate-layer production technology is required. The paper proposes a cable-controlled separate-layer production technology. The cable-controlled separate-layer production system consists of adjustable production regulator, testing and adjusting instrument, ground controller, and some matching tools. In the operation process, the testing and adjusting instrument is run into the wellbore through cable. The locator of the instrument can fix the accurate position where the target regulator is. After the delivery of the instrument, the testing and adjusting instrument connects with the adjustable production regulator. The liquid flow rate of the regulator can be adjusted continuously according to the instructions and the flow rate can be read simultaneously on the ground. The pressure and water cut of the single layer can also be monitored. Once the testing and adjusting of the target regulator are accomplished, the instrument disconnects with the regulator and move on to the next layer under the command from the ground. Field tests showed that the technology realized production adjusting and parameter testing of each layer in the producers. This technology requires the producers to possess well-preserved casing tube and annular testing condition. The technology is applicable to the rod pumped wells with big water cut variation, and the important wells whose reservoir need to be specially monitored. Because the testing and adjusting instrument is run into wellbore through annulus, the operation can be implemented while the pump unit is working, without interfering normal production. The cable-controlled separate-layer production technology effectively relieves the planar, inter layer and interior layer production contradictions. The balanced production of all kinds of reservoirs is realized and the producing capacity of medium-low permeability reservoirs is released, improving production rate and oil recovery.
WanFu, Zhou (Daqing Oilfield Co. Ltd) | ZhongLian, Han (Daqing Oilfield Co. Ltd) | Gang, Cao (Daqing Oilfield Co. Ltd) | Xin, Wang (Daqing Oilfield Co. Ltd) | QingGuo, Wang (Daqing Oilfield Co. Ltd) | WenJiang, Chen (Daqing Oilfield Co. Ltd) | QingSong, Li (Daqing Oilfield Co. Ltd) | JingMei, Wang (Daqing Oilfield Co. Ltd) | Yang, Han (Daqing Oilfield Co. Ltd) | HaiRong, Fu (Daqing Oilfield Co. Ltd)
In the later stage of development, most oilfields faced high water cut issue after treatments. Meanwhile, how to effectively control oil wells water breakthrough after fracturing so as to increase oil production has become a big challenge for production engineers. This paper introduced a novel selective proppant which can effectively block water from entering well bore after fracturing.
Based on "eggshell principle" and interfacial tension theory, this novel proppant was developed with a new monolayer strong hydrophobic interface treatment technique. This special processing technique could not only reduce the proppant's flow resistance of oil, but also increase its flow resistance of water. As the result, this novel proppant showed the characteristics of excellent lipophilicity and hydrophobicity as well. Experiments indicated that oil water diversion ratio of selective proppant was greater than 1.2, while the ordinary proppant was less than 0.7. The oil wettability index of selective proppant was greater than 0.8, while the ordinary proppant was less than 0.3. The main characteristics of this supporting agent was small apparent density, low broken rate, and high flow capacity. The proppant surface is oil wet, which has the characteristics of oil increasing precipitation. Experiments showed that the seepage velocity of water in selective proppant was obviously lower than in quartz sand, selective proppant with water resistance.
Field test was carried out in 11 wells with selective proppant fracturing. A group of conventional fracturing wells were selected as contrasted wells with similar reservoir and operating conditions. After fracturing with novel proppant, the average water cut of producers was decreased by 7.2% per well, the average oil production was increased by 6.3 tons per well, and the average valid fracturing a period was 14.1 months. As for contrasted wells with conventional fracturing proppant, the average single well water cut decline was only 0.4%, the average single well daily oil 3.1 tons, an average period of only 5.8 months.
The novel proppant showed remarkable advantages in improving oil production and decreasing water cut. This technique has a great future for mature oilfield development.
Jiecheng, Cheng (Daqing Oilfield Co. Ltd.) | Wanfu, Zhou (Daqing Oilfield Co. Ltd.) | Yusheng, Zhang (Daqing Oilfield Co. Ltd.) | Xu, Guangtian (Daqing Oilfield Co. Ltd.) | Ren, Chengfeng (Daqing Oilfield Co. Ltd.) | Zhangang, Peng (Daqing Oilfield Co. Ltd.) | Bai, Wenguang (Daqing Oilfield Co. Ltd.) | Zongyu, Zhang (Daqing Oilfield Co. Ltd.) | Xin, Wang (Daqing Oilfield Co. Ltd.) | Fu, Hairong (Daqing Oilfield Co. Ltd.) | Qingguo, Wang (Daqing Oilfield Co. Ltd.) | Xianxiao, Kong (Daqing Oilfield Co. Ltd.) | Lei, Shi
ASP flooding in Daqing oilfield commenced from 1980s. To date, industrial pilot tests have been carried out in three blocks. The averaged recovery was increased by 20%. On the other hand, scaling issue caused high frequent pump failures. Large amount of scale building up in the producers wellbore and downhole equipments with high speed, which resulted in the averaged running life of lifting system decreased from 599 days of water flooding period to 60 days. Further more, some producers' running lives were only around 30 days, leading to higher production cost and lower production rate as well.
Study indicated that, the scaling principle and scale composition in producing wells differed from each other and was difficult to be predicted accurately. In this study, after tracking and measuring the ion in produced fluid for the whole process from water flooding, polymer flooding to ASP flooding and analyzing composition of the scale on different parts of scaling well, the criterion and distinguishing chart of scaling tendency had been set up initially. The criteria were applied in 102 wells in ASP flooding area, the accordance rate was more than 90 percent. Based on that, scaling inhibition technology was timely performed for predicted scaling wells, and the running lives were increased from 40 days to above 200 days. This paper presented the process of the study and is greatly helpful for APS flooding in commercial scale.
Liu, Xiangbin (Daqing Oilfield Co. Ltd.) | Xin, Wang (Daqing Oilfield Co. Ltd.) | Li, Guo (Production Engineering & Research Institute of Daqing Oilfield Company Limited) | Zhang, Limei (Production Engineering & Research Institute of Daqing Oilfield Company Limited) | Han, Zhonglian (Daqing Oilfield Co. Ltd.) | Wang, Bing (Production Engineering & Research Institute of Daqing Oilfield Company Limited)
Due to the prone gas breakthrough in CO2 immiscible flooding, the development effect was poor. In order to block off gas breakthrough channels, improve gas injection/production profile, and increase sweep volume & efficiency, two different acid-resistant and oil-resistant foam systems were developed according to reservoir characteristics and fluid features in Daqing peripheral oilfield. The foam system swelled 4times, the half-life was 83h, and core resistance coefficient was 120 under the condition of PH=3 and 60% oil saturation. Filed test results showed that the systems can effectively block off gas channels, decrease inefficient circulation, increase CO2 sweep volume & efficiency as well as displacement efficiency. The tested well gas injection pressure rose by 3.5MPa after resuming injection. Dominant injection direction changed obviously and gas sweep area increased enormously. Connected wells' gas oil ratio decreased with an average valid period of 11 months and cumulative oil increment of 467t. This gas breakthrough blocking off technology is suitable for gas flooding development of Daqing peripheral oilfields which have ultra-low permeability, and has the advantages of high efficiency and low costs. It provides a sound technique support for gas flooding development.
Xiujuan, Yang (China University of Petroleum) | Tongtao, Wang (China University of Petroleum) | Xiangzhen, Yan (China University of Petroleum) | Xin, Wang (CNPC Research Institute of Petroleum Exploitation and Development)