An economic production scheme for gas shale demands a better understanding of gas flow behavior and a proper reservoir simulator. The complex fracture network and multi-scale flow channel intensify the complexity of gas flow behavior. This paper integrated an improved shale-gas transport model with the extended finite element method (XFEM) to characterize the main flow mechanisms and discrete fracture network. The gas shale was viewed as the dual permeability porous media with discrete fractures. The discrete fractures are not required to be meshed, which can be placed anywhere with given location, length, and orientation. Rock deformation is implicitly coupled with gas flow to reflect stress sensitivity of gas shale. Furthermore, the displacement and matrix pore pressure across fractures are treated as discontinuous by using enrichment approximation functions. The computer coding of proposed model was developed. Terzaghi's problem for dual permeability media was considered to validate the code. The results show that pressure field is disturbed by the discrete fractures obviously, which is compared with regular pressure field obtained from the continuous fracture model. Therefore, it is important to account for discrete fractures for the fractured porous media. One case study of shale gas reservoir was presented to improve the model application. Two patterns of fracture networks were simulated in the rectangular reservoir. It is evident that the orthogonal fracture network is an ideal pattern contrast to the oblique fractures, since the former makes the pore pressure field depleted symmetrically. Furthermore, the stimulated area is the main factor to control the pressure depletion. The results confirm that the presented model and code is capable and flexible to simulate shale gas reservoir with discrete fracture network. This work provides an alternative workflow for parameter designs of hydraulic fracture and production scheme.
Fu, Jiasheng (China University of Petroleum) | Li, Gensheng (China University of Petroleum) | Shi, Huaizhong (China University of Petroleum) | Niu, Jilei (China University of Petroleum) | Huang, Zhongwei (China University of Petroleum)
On the basis of the analysis of the jet-modulating mechanism, a novel tool--a hydraulic-pulsed cavitating-jet generator (HPCJG)--is designed to further improve the rate of penetration (ROP). The HPCJG combines the advantages of a pulsed jet and a cavitating jet. When the drilling fluid flows through this tool, the fluid will be modulated to the pulsed and cavitating jet by application of the impellers and by entering into the self-resonant chamber. During this process, a pulsed cavitating jet is formed at the outlet of the bit nozzle. Because of jet pulsation, cavitating erosion, and the local negative-pressure effect, the cleaning efficiency of the well-bottom cuttings and the ROP will be improved. Laboratory and oilfield tests have indicated that the pulsed-pressure amplitude and the pressure drop of the generator increase with the increase of the flow rate. However, the frequency of the pressure pulsation is invariable in this process. This generator has been applied to more than 100 wells in eight oil fields throughout China. The results show that the maximum density of the test drilling fluid is 1.93 g/cm3, the maximum test-well depth is 6162 m, and the operation time of the generator is more than 230 hours (the maximum operation time recorded was more than 520 hours). Furthermore, the average ROP was increased by approximately 16.7% to 104.4%. In conclusion, the generator has the characteristics of a simple structure, has a long lifetime, is able to adapt well with existing drilling equipment, and can provide a safe and efficient drilling technique for deep wells.
Dou, Liangbin (China University of Petroleum Beijing) | Li, Gensheng (China U. of Petroleum Beijing) | Shen, Zhonghou (China University of Petroleum Beijing) | Song, Xianzhi (Tarim Oil Field Branch) | Du, Tao (China U. of Petroleum Beijing) | Chi, Huanpeng
With the deepening of oil & gas reservoirs exploration and development, an increasing number of sour-gas reservoirs especially those with high content of H2S are developed in the world. Phase transition of high-sulfur gas or H2S will be easy to occur near the wellhead, and bottom-hole pressure reduces drastically, which possibly leads to serious blowout. Considering the special physical properties of high-sulfur gas and its possible phase transition in the wellbore, a mathematical model for wellbore flow and heat transfer during formation high sulfur gas invasion was established. The heat transfer and pressure were coupling calculated along with high-sulfur gas physical properties parameters, and a solution method of the model was proposed. The wellbore pressure and properties of gases with different content of H2S rising process along the wellbore were analyzed. The reason of high-sulfur gas easy to result in the problem of well control was presented. The paper exhibited the results of the bottom-hole pressure and depth of phase transition varying with different influx rate, injection rate, choke pressure and land surface temperature, and the reasons of wellbore pressure and phase transition influenced by these operating parameters were discussed respectively. The study is of certain significance for improving the safety of acidic oil & gas reservoirs exploration and development.
Li, Gensheng (China University of Petroleum Beijing) | Sheng, Mao (China University of Petroleum Beijing) | Tian, Shouceng (China U. of Petroleum Beijing) | Huang, Zhongwei (China University of Petroleum, Beijing) | Li, Yuanbin (PetroChina Tarim Oil Field Company) | Yuan, Xuefang (CNPC)
The placement of multiple fractures in deep horizontal wells is more difficult than that in shallow formations due to HTHP conditions. This paper presents the latest advances in hydra-jet acid fracturing for solving problems in the process of deep well
acid fracturing. Basic researches and application evaluations were conducted to overcome down-hole conditions. Special schedule was designed delicately to lower the cracking pressure. The jet velocity was increased more than 800ft/sec to enhance the penetration efficiency. Acid pad fluid also was jetted to the target point for 15 minutes to erode carbonate rock, which leads to lower the rock strength. An explanation how to execute process has been included in details. The different procedures of treatment in shallow and deep reservoir were also discussed.
A novel hydra-jet acid fracturing job was performed with great success on two horizontal wells in an ultra deep carbonate reservoir in China. Seven separated acid fractures were placed along horizontal section from 19,816.3~21,056.4ft in one well
and a large total acid volume of 21,824.5ft3. After acid fracturing, the well produced naturally high rate of 251~314STB/D. The other well is completed with un-cemented liners and the deepest treatment was applied at the TVD of 20,999.1ft. Four
separated fractures were achieved along the 656.17ft lateral section. The pump pressure was controlled in the scope of predicted value (Below 10,000psi).
The main finding is that the hydra-jet acid fracturing has two mechanisms. The first is the hydraulic dynamic sealing effect and the second is the reduction of the time of acid-rock reaction to extend the effective distance. An addition, hydra-jet acid
fracturing method proved the effectiveness of delivering acid fractures in the ultra deep horizontal wells.
Horizontal drilling and multistage stimulation technologies are becoming popular to develop the lime reservoir. The Tarim ultra deep lime formation is no exception. Natural cave and fractures are the key reserve strctures for these reservoirs. Horizontal drilling and hydraulic fracturing enables the well to intersect with natural fractures in this area extensively1. Since limestone is consolidated and stable, many wells in the Tarim lime formation are completed with preperforated liners. Unfortunately, there is almost no effective way to fracture liners completion using conventional means because of wellbore isolation problem. Besides, high pressure and high temperature (HPHT) conditions cannot be disregarded in the ultra deep
reservoir, which further exacerbates the job challenge.
Song, Xianzhi (China University of Petroleum Beijing) | Li, Gensheng (China University of Petroleum Beijing) | Huang, Zhongwei (China University of Petroleum, Beijing) | Zhang, Laibin (China University of Petroleum, Beijing) | Tian, Shouceng (China U. of Petroleum Beijing) | Cui, Liu (CNPC Drilling Research Institute)
Horizontal wellbore cleanout by rotating jets has been developed rapidly in the past decade. However there are few investigations on mechanism and characteristics of the high pressure water jet impacting and annular helical flow, which are two primary powers to break up the consolidated bed, lift and suspend particles, and increase the wellbore cleanout efficiency. To realize the characteristic of helical flow, the pathilines of rotating high pressure jets and annular velocity distributions were
investigated firstly in this paper. The results indicated that the motive power to form the annular helical flow is the non-uniform cross flow generated by partial lateral jets which impact on the wall at an angle, while other jets provide the fluid sources. Further, base on the particle trajectory model and liquid-solid mixture model, the motions of particle, the annular distribution of sand velocity and concentration in annular helical flow were carried out. The pathlines of sand were spiral curves around the drill pipe in the annular helical flow, which can enhance the sand moving ability and increase the horizontal wellbore cleanout efficiency finally. The influences of flow rate, particle size, nozzle assemblies on the annular helical flow strength and sand transportation efficiency were analyzed comprehensively. Finally, the downhole tool was designed according the theoretical results and has been tested in hundreds wells in China. The test showed that it can greatly improve the oil and gas well production and reduce the operating duration. This paper is beneficial to investigate characteristic of sand sweeping by annular helical flow and optimize the tool structure, operation parameters.
Li, Gensheng (China U. of Petroleum Beijing) | Haizhu, Wang (China U. of Petroleum Beijing) | Zhonghou, Shen (China U. of Petroleum Beijing) | Song, Xianzhi (China U. of Petroleum Beijing) | Guanwei, Tang (China U. of Petroleum Beijing) | Xinjuan, Hou (Harding Shelton Group Energy Consulting (Beijing) Limited)
Supercritical carbon dioxide (SC-CO2) has the characteristics of high density, low viscosity and high diffusivity, and higher penetration rate can be achieved with SC-CO2. But the law of cuttings carrying is not clear, in order to make clear the influence of pump displacement, well incline, cuttings diameter, wellbore temperature and pressure on cuttings carrying efficiency, the laboratory experiments was carried out to simulate the cuttings carrying with SC-CO2 in annulus. The result shows that the cuttings carrying efficiency decreases when pump displacement decreases and cuttings diameter increases, and it decreases with the increasing of well incline at first, and then increases. Wellbore temperature and pressure have much more influence on cuttings carrying efficiency, and it decreases when the wellbore pressure increases, if keeping the wellbore temperature and pump displacement in constant; and it increases when wellbore temperature increases, if keeping the wellbore pressure and pump displacement in constant. So the wellbore temperature can be adjusted to compensate the cuttings carrying efficiency's changes caused by pressure changes, and the excess annulus velocity should be in consideration to avoid erosion of casing, drilling pipe and other down hole tools.