Zhou, Jian (State key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Sinopec Research Institute of Petroleum Engineering) | Zeng, Yijin (State key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Sinopec Research Institute of Petroleum Engineering) | Jiang, Tingxue (State key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Sinopec Research Institute of Petroleum Engineering) | Zhang, Baoping (State key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Sinopec Research Institute of Petroleum Engineering) | Shen, Boheng (Missouri University of Science and Technology) | Zhou, Jun (State key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Sinopec Research Institute of Petroleum Engineering)
ABSTRACT: The multi-staged fracturing is becoming one of the key strategies for the shale gas development worldwide. The impact of stress shadow and natural fractures on fracture could cause unexpected fracture geometry in this case. The staged fracture initiation and fracture geometry during fracturing in shale are investigated through a series of tri-axial fracturing experiments. The shale blocks made by fresh shale outcrop were tested with a varied of perforation intervals as 80mm, 120mm, 160mm, 200mm, respectively. The testing results demonstrated that the multi-fracture interference occurred and it caused complex unbalanced facture geometry when the notch interval was 80mm and 120mm. By real-time diagnosis with microseismic(MS) data, we found that due to the double effect of stress shadow and natural fracture, the second fracture tends to be much shorter compared with the first fully developed fracture. Meanwhile, the direction of the second fracture tends to be a diverging fracture. However, the obvious effect of stress shadow was not found in our tests when the notch interval was 160mm and 200mm. At last, a simple mode for effective stimulation of reservoir volume (ESRV) calculation based on MS data was introduced to compare individual ESRV for different fracture geometries.
With the development of shale gas in the last decades, horizontal multi-stages hydraulic fracturing have more and more become valuable technique for stimulation of shale reservoirs. In naturally fractured shale reservoirs, the widely held assumption that the hydraulic fracture is an ideal, simple, straight, bi-wing, but planar feature is untenable because of natural fractures, faults, bedding planes and stress contrasts. In this kind of shale reservoirs due to interaction with natural fractures or frictional interface, the fracture may propagate asymmetrically or in multiple strands or segments.
The presence of natural fractures alters the way the induced fracture propagates through the rock. The early studies (Zoback, 1977; Daneshy, 1974; Lamont and Jessen, 1963; Blanton, 1982) have shown that the propagating fracture crosses the natural fracture, turns into the natural fracture, or in some cases, turns into the natural fracture for a short distance, then breaks out again to propagate in a mechanically more favorable direction, depending primarily on the orientation of the natural fracture relative to stress field. A fracture interaction criterion to predict whether the induced fracture causes a shear slippage on the natural fracture plane leading to arrest of the propagating fracture or dilates the natural fracture causing excessive leak-off was proposed based on mineback experiments (Warpinski and Teufel, 1987). A simple criterion for crossing was proposed by applying a first order analysis of the stresses near a mode I fracture impinging on a frictional interface oriented normal to the growing fracture (Renshaw and Pollard, 1995). According to their work, crossing will occur if the magnitude of the compression acting perpendicular to the frictional interface is sufficient to prevent slip along the interface at the moment when the stress ahead of the fracture tip is sufficient to initiate a fracture on the opposite side of the interface. Scaled laboratory experiments and numerical tests proved that high flow rate or viscosity yields fluid- driven fractures, while low flow rate just opens an existing fracture network (Beugelsdijk and de Pater, 2000, 2005). Laboratory scale tests also found that interaction of a hydraulic fracture with a natural fracture depended heavily on the stress state, inclination of the natural fracture with respect to the hydraulic fracture, and the strength of the natural fracture (Zhou et al., 2010 and Ingraham et al., 2016). For the case of natural fractures in shale are mineralized, researchers embedded planar glass discontinuities into a cast hydrostone block as proxies for cemented natural fractures and used these blocks to perform tests to examine the effects of cemented natural fractures on hydraulic fracture propagation. Their results show that obliquely embedded fractures are more likely to divert a fluid-driven hydraulic fracture than those occurring orthogonally to the induced fracture path (Olson et al., 2012).
Jiang, Tingxue (Sinopec research Institute of petroleum enginering) | Zhou, Dehua (Sinopec) | Jia, Changgui (Sinopec research Institute of petroleum engineeing) | Wang, Haitao (Sinopec research Institute of petroleum engineeing) | Bian, Xiaobing (Sinopec research Institute of petroleum engineeing) | Li, Shuangming (Sinopec research Institute of petroleum engineeing) | Xiaobo, Xiaobo (Sinopec research Institute of petroleum engineeing) | Weiran, Weiran (Sinopec research Institute of petroleum engineeing) | Suyuan, Suyuan (Sinopec research Institute of petroleum engineeing)
In the end of 2012, the breakthrough of 15 stages fracturing treatment of horizontal well-JiaoYe 1HF, located in Jiaoshiba block, Fuling gas play, Chongqing, China, with the post-fracturing gas production 203,000 m3/d (
A systematic method was employed in this study which contains physical simulation in lab, numerical simulation, and fracturing fluid additives development as well. Firstly, a comprehensive formation evaluation was conducted such as rock lithology, pore throat size, porosity, permeability, rock mechanics, three dimensional stress, pore structure, maturity, total organic content, total gas content including free gas and absorbed gas, etc (
The above mentioned technology have been applied in a large scale (more than 200 wells) in Fuling shale gas play, therefore, expected results are obtained with the average gas production more than 300,000 m3/d, and the highest open flow capacity as high as 1,580,000 m3/d. Now, Fuling shale gas field is the largest one in China, its annual production is more than 5 billion m3.
Therefore, it has a great significance on the hydraulically fracturing technology in other lithology such as tight sandstone and carbonate reservoirs.
Zhou, Jian (Sinopec Research Institute of Petroleum Engineering) | Zeng, Yijin (Sinopec Research Institute of Petroleum Engineering) | Jiang, Tingxue (Sinopec Research Institute of Petroleum Engineering) | Zhang, Baoping (Sinopec Research Institute of Petroleum Engineering) | Zhang, Xudong (Sinopec Research Institute of Petroleum Engineering)
This reservoir is a tight gas field and the target sand stone zones are generally staged fracturing treated at depths of roughly 1500 to 2800 meter. Knowing the direction or azimuth of the fracture orientation is important in development of this low permeability reservoir with horizontal wells. The paper presents surface tiltmeter hydraulic fracturing mapping results of 15 stages treatment in two horizontal wells at the same operational period. The two wells are part of a cluster of six horizontal wells located in North of Yulin, Shanxi province. Application of this technology is important in this tight gas field where fracture stimulation is a key method for production enhancement and reservoir development. This was the first deployment of tiltmeter mapping on a cluster of horizontal wells, and several modifications were made for the standard procedures. Using an array of 54 Surface Tiltmeters, the mapping was performed on all 15 treatments with the average perforation depths of TVD 2540 to 2545m at each horizontal section to determine hydraulic fracture azimuth and fracture length, respectively. For the first horizontal well R-3H, the tiltmeter mapping results show that, the azimuth of fractures is between N53 °E and N71 °E, and the fracture half length for stages fractures is between 112m and 149m. For the second horizontal well R-5H the tiltmeter mapping results show that, the azimuth of fractures is between N67 °E and N76 °E, and the fracture half length for stages fractures is between 107m and 142m. Besides, in the well R-3H from stage 7 to stage 9, the horizontal volume component of fractures, increased from 17% to 34%, as well as in the well R-5H from stage 5 to stage 9, the horizontal volume component of fractures significantly increased to 69% from 20%. Meanwhile, the production of the two wells after the fracturing was the first and second among the cluster of the six horizontal wells, respectively. Thus, by using the synchronous fracturing technology, we believe that it not only improved the complexity of the staged fractures between the two wells but also led to a better production enhancement.
Jiang, Tingxue (Sinopec Research Inst. of Petroleum Engineering) | Zhao, Xiaoxiang (Sinopec Research Inst. of Petroleum Engineering) | Yin, Fei (China U. of Petroleum, Beijing) | Qu, Hai (Sinopec Research Inst. of Petroleum Engineering)
Multistage hydrajet-fracturing(MHJF) combines hydrajet perforating and hydraulic fracturing to perform separate, sequential fracture stimulations without mechanical packers. It can reasonably place fractures according to geological condition, and then accurately treat them. Without packer, it uses dynamic isolation to seal flow into target, saving operating time and lowering operating risk. Therefore, the process not only especially adapts to cement casing completion, but effectively treats slotted liner completions.
The mechanisms and fluid dynamics of multistage hydrajet-fracturing technology are investigated with numerical simulation and laboratory experiments. Three horizontal wells with slotted liner completion have been successfully treated using this technology. The detailed interpretation about resolve plans will be including in this paper. In order to prevent sanding pipes easily happening in horizontal section of slotted liner, hydrajet fracturing technology were optimized to decrease the risk in treatment process. On average, three hydraulic fractures were placed at strategically selected locations in well, typically several hundred meters apart without sealing equipments. And also, the microseismic mapping data indicated that three oblique fractures were obviously created at the fracturing locations which improved the formation permeability. This paper will deeply review three field applications where MHJF technology was used to the slotted liner completion.
Significant stimulation results were achieved in these wells. For example, production increased by more than 50 times after stimulation to the gas well XS311H in Sichuan oilfield. The oil well 92-2 in the ZhongYuan
oilfield, which had been a dead horizontal well, has been revived using this technology with average oil production of 15 tons per day.
Lei, Qun (PetroChina Co. Ltd.) | Jiang, Tingxue (PetroChina Co. Ltd.) | Xu, Yun (PetroChina Co. Ltd.) | Ding, Yunhong (PetroChina Co. Ltd.) | Lu, Yongjun (Langfang Branch of RIPED) | Bo, Cai (Research Inst. Petr. Expl/Dev) | Shu, Yuhua (Langfang Branch of RIPED) | Duan, Yaoyao (Research Inst. Petr. Expl/Dev)
There are a lot of tight gas formations with high temperature and high pressure in the south of Songliao basin in northeast China. However, it is very difficult to conduct successful fracturing treatment jobs as results of deep wells (more than 4200 m), high temperature (more than 150°C) and high pressure (more than 60 MPa), etc. Therefore, a systematic studies have been performed to overcome above mentioned difficulties, and the highlights are: 1) Fine formation evaluations prior to fracturing treatment; 2) A new finely processed Guar is developed, and the concentration is only 0.45% for the temperature of 150°C, and residue content 125 mg/l correspondingly, both are much less than those of commonly used Guar system; 3) Smaller sized proppant with high strength is optimized, sometimes, more than two proppant types or sizes is also chosen comprehensively; 4) Fuzzy undetermined analysis of economic benefit is performed to optimize propped fracture length and conductivity, in which the Monte-Carlo method is utilized; 5) Many fracturing treatment parameters are changed and combined optimizedly such as proppant's type and size, fracturing fluid's type, cross linked ratio, concentration of based fluid, concentration of gel breaking agent, and pumping rate as well, which makes it not only to ensure the successful treatment but also to minimize fracture damage so as to maximize fracturing treatment potential; 6) Spiral mode of proppant pumping schedule is put forward in order to prevent earlier screen-out; 7) A new forced fracture closure technique is utilized to improve propped profile in the case of multiple payzones. Above low damage and massive fracturing technique was put in to filed applications in 6 gas wells, all treatments were completely successful with the maximal proppant weight being as high as 165,000 kg, while in the past, there were many treatment failures. And the highest post-fracturing rate 70,000 m3/d,which is satisfied as expected. So, it has a great significance not only in improving fracturing treatment effect in above mentioned gas formations but also in perfecting low damage and massive hydraulic fracturing technique as well.
There are many difficulties related to hydraulic fracturing design and treatment in tight gas formations with high temperature and high pressure, such as formation's fine evaluation, fracture and propagation of hydraulic fracture, selection of low damage and high viscous-elastic fluid, selection of high strength proppant easily being transported, many fracturing treatment failures encountered as a result of early tip screen-out, etc. In the past, the commonly utilized fracturing technique may be summarized as following: 1) Ordinary Guar fluid with relative high polymer concentration and high residue content; 2) Medium proppant size of 20-40 mesh; 3) Common proppant pumping schedule such as 180 kg/m3-360 kg/m3-540 kg/m3-720 kg/m3-900 kg/m3; 4) longer time of shut-in for at least 2 hours. Consequently, the post-fracturing rate is disappointed, and what the production potential of tight gas formations has been kept as unknown for a long time.
Therefore, a low damage and massive hydraulic fracturing technique was studied in detail comprehensively based on systematic investigation of recent hydraulic fracturing advancement all over the world.
Furthermore, some new design considerations and treatment measures are put forward in the paper according to the specific characteristics of the targeted gas wells. So, it may ensure not only the successful placement of bigger sum of proppant weight but also the maximal performance potential of the formation.
Lei, Qun (Langfang Branch of RIPED) | Ding, Yunhong (Langfang Branch of RIPED) | Jiang, Tingxue (RIPED of PetroChina) | Xu, Yun (PetroChina Co. Ltd.) | Song, Shemin (development department of Huabei oil field, PetroChina) | Liu, Yanxue (North-east Project Department, PetroChemical) | Cai, Bo | Duan, Yaoyao
The characteristics of exploration zones in China in recent years are summarized as: 1) Special lithology such as volcano and clay-carbonate, etc. 2) low porosity and ultra-low permeability; 3) Complex storage types and fluid flow mechanics as a result of natural fractures distributed stochastically; 4) Special in-situ stress and loss characteristics; 5) complex rock mechanics and elastic-plastic traits; 6) Undetermined fracture height growth; 7) complex stress sensitivity. Therefore, a systematic technologies are put forward in the paper, the highlights are: 1) Systematic formation fine evaluation which contains Nuclear Magnetic Resonance, Constant Rate Mercury Injection and so on; 2) Low damage fracturing fluids such as super grade Guar fracturing fluid and its combination with liquid nitrogen, low cost VES(less than 300 RMB below 90°C), low polymer concentration fracturing fluid and linear gel, and variable viscosity is utilized in different treatment stage; 3) Different type and diameter proppants are used in one treatment job, and the combined ratio is optimized; 4) A new method of multiple stage optimization is put forward to ensure not only the success of stimulation treatment but also the maximal post-treatment performance; 5) Counter measures are applied systematically such as two combinations of pumping rate and viscosity to control loss and multiple fractures, fracture height control, systematic quality control and post-treatment management, etc. What's more, above technologies have been put in to field applications in more than 39 wells in the year of 2005, and the result is satisfied with the newly increased oil reserves being greater than 1×108 t, gas reserves greater than 800×108 m3. Consequently, it has a great significance in China's main exploration zones, in the mean time, it also has a great benefit of economy and hydraulic fracturing and acidizing themselves.
Nowadays, more and more low permeability exploration wells are drilled in recent years in China. According to statistics, more than two third of oil and gas reserves discovered annually is low permeable reservoirs (seen in figure 1) which must apply hydraulic fracturing and acidizing so as to determine the reserves grade or formation characteristics thoroughly.
Jiang, Tingxue (RIPED of PetroChina) | Zhang, Yiming (Huabei Petr. Admin. Bureau) | Wang, Yongli (RIPED of PetroChina) | Ding, Yunhong (Langfang Branch of RIPED) | Luo, Ning (PetroChina Co. Ltd.) | Xu, Zejun (Huabei Oil Field Corporation,PetroChina) | Feng, Xingkai | Zhang, Hongmei
However, the post treatment effect is far away from satisfaction as a result of high closure stress and high temperature. Therefore, hydraulic fracturing is used as an alternate technique in order to achieve longer stable rate after stimulating treatment. One advantage of hydraulic fracturing is that it can sustain high closure stress by virtue of propped proppant within the artificial fracture; the other is that it can obtain a longer fracture length, so, theoretically, the optimum selection is to utilize hydraulic fracturing in the case of the ensuring of hydraulic fracturing treatment success. Enlightened by the successful application of hydraulic fracturing in carbonate oil bearing reservoirs in Tarim oil field, China, a pilot field test of hydraulic fracturing in claycarbonate reservoirs is conducted in Shulu cave, located in Huabei oil field.
Jiang, Tingxue (RIPED of PetroChina) | Wang, Yongli (RIPED of PetroChina) | Ding, Yunhong (Langfang Branch of RIPED) | Zhang, Yiming (Huabei Oil Field Corporation,PetroChina) | Xu, Zejun (Huabei Oil Field Corporation,PetroChina) | Zhang, Hongmei (Huabei Oil Field Corporation,PetroChina)
In low permeable exploration wells, how to minimize formation damage and fracture damage is regarded as an unique goal of hydraulic fracturing design and treatment. Sometimes, an inappropriate fracturing design may even decrease an exploration wellâ€™s oil production potential as a result of high damage within both formation and fracture, so that an error decision-making may be determined. Therefore, a new fracturing technology of low damage for exploration wells is put forward in the paper, compared with the past conventional fracturing technology, the highlights of the new technology includes: 1) A new concept of damage is established and demonstrated, it contains not only damage as just mentioned above but also excessive fracture height growth, inappropriate proppant propped pattern and so on; 2) utilizing the newly developed fracturing fluids such as slick water, low concentration of densifier, linear gel (not cross linked), low molecular weight fluid, etc.; 3)optimizing the minimum viscosity of fracturing fluid, then optimizing the corresponding pumping rate; 4)studying the optimum combination of fracturing fluid types and that of proppant type and size in the course of fracturing treatment; 5)Studying the sensitivity of formation damage and fracture damage to the post-fracturing performance, which may be used to select fracturing treatment parameters inversely; 6) one of the main optimization target is to minimize fracture propagation length after shut-in so as to obtain an optimized propped profile; 7)studying the mechanism of water blockage during the course of fracturing treatment and the countermeasures correspondingly. Whatâ€™s more, above fracturing technology has been put in to field applications and an expected result has also been obtained, so it has a great significance in improving fracturing technology, reservoir evaluation and reservoir development as well.
Ding, Yunhong (Langfang Branch Institute of Petroleum Exploration and Development of Petrochina) | Jiang, Tingxue (Langfang Branch Institute of Petroleum Exploration and Development of Petrochina) | Wang, Yongli (Langfang Branch Institute of Petroleum Exploration and Development of Petrochina) | Sun, Ping (Exploration Department of North China Oil Field Corporation, Petrochina) | Xu, Zejun (Exploration Department of North China Oil Field Corporation, Petrochina) | Wang, Xin (Langfang Branch Institute of Petroleum Exploration and Development of Petrochina) | Zeng, Bin (Langfang Branch Institute of Petroleum Exploration and Development of Petrochina)
A case study of hydraulic fracturing has been performed in details in Jing-70 gas well located in north china oil field with the depth larger than 4000 meters.In the past,such kind of gas wells couldn't be fractured successfully as a result of early tip-screenout.Our study is on the base of past fracturing experience,and a lot of improvements have been made.The main character of our fracturing design is as following:1)core test of stress sensitivity is used in performance prediction model and determination of bottom flowing pressure;2)mini-frac is performed in order to get loss coefficient more precisely;3)large scale of proppant volume and high proppant concentration are used as principles;4)a new surfactant named DL-10 is developed to increase flowing back velosity;5)long term conductivity is inputted in to a new developed gas reservoir model so as to perform optimization more scientifically;6)multi-stage proppant pumping schedule is used so as to get an expected propped profile;7)pumping rate is requested to increase higher and higher under the limit of wellhead pressure according to three dimensional fracture propagation model;8)liquid nitrogen is used in the course of fracturing in order to enhance flowing back of fracturing fluid after shut-in;9)forced closure technique is utilized;10)systematic field quality control is used to ensure fracturing treatment to follow the design plan,and some modifications is allowed according to the change of treatment situation.After that,the well is hydraulically fractured successfully with 67 tons of proppant and sand to liquid ratio as high as 30%,which is the highest record in ultra-deep gas wells in north china.And post evaluation is performed completely including net pressure analysis.Overall,the fracturing design,treatment and post evaluation discussed in the paper for ultra-deep gas wells has a great significance in gas wells' stimulation and development as well.
Wang, Yongli (Langfang Branch Institute of Petroleum Exploration and Development of PetroChina) | Jiang, Tingxue (Langfang Branch Institute of Petroleum Exploration and Development of PetroChina) | Ding, Yunhong (Langfang Branch Institute of Petroleum Exploration and Development of PetroChina) | Luo, Ning (Exploration Department of North China Oil Field Corporation, PetroChina) | Feng, Xingkai (Exploration Department of North China Oil Field Corporation, PetroChina) | Wang, Xin (Langfang Branch Institute of Petroleum Exploration and Development of PetroChina) | Zeng, Bin (Langfang Branch Institute of Petroleum Exploration and Development of PetroChina)
There are a lot of low permeable and complex reservoirs in china, most of them are undeveloped up to now as a result of difficulties such as stochastic distribution of formation parameters (mainly permeability and thickness), economic risk in hydraulic fracturing decision-making, unsatisfied post-fracturing rate and relatively short effective period of production after fracturing compared with those in conventional reservoirs, etc. Consequently, an expert system of hydraulic fracturing in above mentioned reservoirs is studied in details. It mainly contains:1)Stochastic distribution of reservoir parameters analysis; 2)An advanced neural network is utilized to forecast 3 dimensional fracture geometry and post-fracturing rate(oil and water) correspondingly under various conditions; 3)Monte-Carlo method is used to perform economic risk analysis; 4)Genetic algorithm is applied to automatically select fracturing materials and optimize fracturing treatment parameters such as propant volume, proppant concentration, pumping rate, pad percentage,etc. What's more, above optimized parameters may also be assigned various practical limits. After that, two field cases are demonstrated in details focusing on how to use the expert system and what the results we have got. Actually, the post-fracturing rate, effective period of production after fracturing and economic benefit as well are all very satisfied compared with common fracturing technology applied in the similar reservoirs. Which verifies that the expert system of hydraulic fracturing developed in the paper is not only reliable but also feasible and if it is put in to field applications in a large scale, a lot of time may be saved and the efficiency to perform hydraulic fracturing design and treatment may be much higher than ever before, in the same time, a greater economic benefit may also be available correspondingly. So, the development level in low permeable and complex reservoirs may also be improved a lot with above mentioned expert system in the future.