Yu, lei (CNPC Greatwall Drilling Company Engineering Research Institute) | Yu, Chen (CNPC Greatwall Drilling Company Engineering Research Institute) | Shang, Xianfei (CNPC Greatwall Drilling Company Engineering Research Institute) | Chen, Zhengang (CNPC Greatwall Drilling Company Engineering Research Institute) | Wu, Sheng (CNPC Greatwall Drilling Company) | Zhao, Yun (CNPC Greatwall Drilling Company Engineering Research Institute) | Liu, Yanqiang (CNPC Greatwall Drilling Company Engineering Research Institute)
In view of low possibility across fractures, low controlled reserve for a single well, fast production decline, poor development performance for conventional horizontal well and directional well in the liaohe buried-hill migmatitic granite reservoir with characteristics of deep buried-depth, hard rock formation, fractured low porous and permeability, optimization deployment of variety of multilateral wells increases effective footage in pay zone and achieves better development performance by the spatial distribution of several lateral boreholes in a single well. Many challenges such as casing cutting, suspended sidetrack drilling in open hole and retrieving whipstock in this formation are solved, and that delivers records of window opening at the formation in scale of hardness 8, deepest window depth of 3523m. As of today, 40 multilateral wells have been completed with effect improved 3 times as offset vertical wells, 1.5 times as horizontal well. It becomes an approach to develop such reservoirs due to huge economical benefits.
Zhou, Zongqiang (PetroChina Changqing Oilfield Company) | Cui, Longlian (Drilling Research Institute, CNPC) | Li, Jianmin (Petrochina Changqing oil field) | Zhang, Fucheng (Petrochina Changqing oil field) | Wu, Xuesheng (PetroChina Changqing Oilfield Company) | Ge, Yunhua (China Natl. Petroleum Corp.) | Wang, Haige (CNPC Drilling Research Institute) | Ju, Mancheng (CNPC Drilling Research Institute) | Ouyang, Yong (CNPC Drilling Research Institute)
Advantages of cluster well are that the technology can save land resources, reduce development costs. Sulige gas field is a typical low porosity, low permeability and low abundance. The advantages can meet the requirement of developing and
constructing a "scientific, harmonious and environmental friendly" Sulige gas field. There are some difficulties in cluster wells drilling operation in Sulige gas field as following: strong abrasive formation, difficult in trajectory control, low ROP and high drilling costs.
To address these difficulties and promote the application of cluster well, the following researches were carried out: (1) Optimization the numbers of wells under different cluster well network conditions. Combined average horizontal displacement, anti-collision, trajectory control and integrated the cost, the number of wells were calculated, analyzed and optimized. (2) Optimization casing profile. Casing section was optimized into the current "straight - slow bulid - hold-slow drop"; (3) Optimization the well trajectory control mode. A practical and efficient directional well trajectory control technology were explored, and BHAs were developed; (4) Individual design PDC bits. "Spiral knife-wing, short outside the parabolic shape of the crown, double cutting structure, spiral gage" structure of the PDC bits were designed for Sulige formation.
Through innovative research and field integration applications, cluster well drilling supporting package technology have primarily matured in Sulige gas field. The drilling cycle of cluster well was reduced by 35%, with 17.4d drilling cycle in 2011; the ROP was improved by 106.1%, with 14.9m/h ROP in 2011. By the end of 2011, total 468 cluster well grops have been completed and 750 hectares land were conserved. Through the application of cluster well drilling in Sulige field, the development costs were reduced significantly. Cluster well technology has become one of the major development models in Sulige gas field.
Zhang, Fuxiang (Petrochina Tarim Oilfield Company) | Che, Mingguang (Langfang Branch-Research Institute of Petroleum E&D) | Yang, Xiangtong (Research Institute of Petroleum Engineering,PetroChina Tarim Oilfield Company) | Zhou, Fujian (Langfang Branch-Research Institute of Petroleum E&D) | Yuan, Xuefang (CNPC)
Hydraulic fracturing is a fissured tight gas productive completion technique in KuqaHPHT fieldin Western China, the gas zone is buried in deeper earth's crust in thats and fracruring has been fored to deal with hotter tempetures, higher pressures and higher stess.During past decades, the fracturing stimulations underulta-deep high tempeture high pressure and high stess have been performed for higher yieldsin Kuqagasfield.
This paper provides a brief developed histoty of Kuqa and the characteristics of formations, such as Jura AH sandstones, Paleogene SWY sandstones and Cretaceous BSJQK sandstones.In major, this paper introduces the techniques and experiments necessary for the treatment of adding sand fracture stimulation, including rock mechanical laborary tests and stress profiles, weighted fluids and their performances, resin coated proppant tests, and minifrac diagnotics that are performed to help designer an effective approach for fissured high stress hydraulic fracturing.In addition, frac string,140MPa fracturing equipment and 140MPa well head, which are the countermeasures of high treatment pressure,are discussed in this paper. Fianl, examples of proppant fracturing treatments are included, and the deepest fracturing reservoir is neighbor to 7000m, the continuous high surface pressure is over 120MPa.
The production of fracturing wells is excited in the fissured high stress tight gas field of Kuqa. Many components of this paper may be helpful for those preparing for a HPHT high stress treatment.
Liu, Bingshan (Research Institute of International Technologies of CNPC Drilling Research Institute) | Wang, Xi (CNPC Drilling Research Institute) | Li, Wanjun (CNPC DRI) | Zhang, Shaoyun (CNPC Drilling Research Institute) | Dong, Jianhui (CNPC Drilling Research Institute) | Yang, Yuping (CNPC DRI)
Arum River Basin is a large scale sedimentary basin lying in the southeast of Tejen platform. Amu Darya right bank is situtated between Amu Darya and the border of Turkmenistan and Uzbekistan. There are several difficult problems in the drilling of this area: overpressured gas reservoir, shallow secondary gas pool with ultra-high pressure, high pressured saltwater layer and high tempreture of bottom hole and so on. So the success rate of the more than 200 wells drilled by the oil companies of Former Soviet Union and Turkmenistan is less than 30%.
We solved these problems by optimizing borehole structure, optimizing drilling fluid system and strenthenning the system of well control etc.. Up to 2010, more than 50 wells were drilled successfully in this area. The success rate is 100%. It is a great break in the drilling of Amu Darya right bank area.
Key words: overpressured gas reservoir, shallow secondary gas pool, high pressured saltwater layer
1.1 Geographical position
Arum River Basin is a large scale sedimentary basin lying in the southeast of Tejen platform. Amu Darya right bank is situtated between Amu Darya and the border of Turkmenistan and Uzbekistan (Fig.1).
1.2 Geological stratification
The cover depth of main gas reservoir is of 2500-4000m. The thickness is about 300-400m. It is deepen step by step from west to east. Gas pool cover depth of contractual block A and northwestward ilijik (block B), eastern Akgumolam (block B) is below of 3000m. The cover depth of the rest of block B is about 3000-4000m. The geological stratification from the bottom to the top contains lower-middle Jurassic structural, Cretaceous structural, lower Tertiary, upper Tertiary and Quaternary. The formation lithology mainly contains shale, sandstone, gypsum, halite, limestone and carbonate rock.. The main target formation is the Callovian- Oxfordian stage of upper Jurassic.
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.
Xia, Yan (China University of Petroleum Beijing) | Shen, Ruichen (CNPC Drilling Research Institute) | Yuan, Guangjie (CNPC Drilling Research Institute) | Zheng, Lihui (China University of Petroleum Beijing) | Tian, Maofa (CNPC Bohai Drilling Engineering Company Limited) | Li, Jingcui (CNPC Drilling Research Institute)
For the characteristics of low pressure and low permeability of coal reservoir in China, conventional drilling may damage reservoirs and reduce the production of CBM. In order to find efficient drilling technology used for CBM development, three
kinds of under-balanced drilling technologies, gas drilling, aerated liquid drilling and circulated micro-bubble drilling have been used for CBM development. Considering the different characteristics of three kinds of under-balanced drilling
technologies, firstly, by analyzing the use of gas drilling, characteristic of coal seam and technical measures for gas drilling, besides that, considering the characteristics of CBM and the state of drilling technology in China, the feasibility of gas drilling technology used in China's CBM development. Secondly, the research result and field application of aerated liquid and circulated micro-bubble under-balanced drilling technique are introduced. In the end, the importance of under-balanced drilling for reservoir protection and layer-loss prevention is stated.
Chen, Peng (CNPC Drilling Research Institute) | Cheng, Cunzhi (China National Petroleum Corp.) | Xin, Junhe (PetroChina Co. Ltd.) | Wang, Xi (CNPC Drilling Research Institute) | Ye, Dongqing (CNPC Drilling Research Institute) | Feng, Guoliang (CNODC,CNPC)
This paper presents a case history on drilling of an ultra-deep exploratory well with a lot of problems and final solution in a complicated K structure in Uzbekistan. Drilling troubles include serious stuckpipe resulted from drilling-in the unexpected
high pressure brine formation, malfunction of the high density drilling fluid system, and subsequent failure of the fishing jobs, unsuccessful sidetracking, bad job of cementing, etc.
After the drilling fluid system was improved, the high pressure layers were isolated, and the proper drilling measures were carried out, the second sidetracking gained success and the well was completed. Afterwards, an adjacent ultra-deep well in
the same structure was smoothly drilled and completed by means of optimization of the casing programs, drilling fluid system and technical measures.
Drilling practices of previous offset well indicated that the formation is pay zone and produced oil, while the same formation at the same depth in the well JD3# produces brine water, which resulted in overflow during twice sidetracking of the same
formation. The high and low pressure layers existed in the same section after drilling-in brine formation would produce complex against drilling and subsequent operations, therefore a 7-inch liner was set to isolate the high pressure formation, so
as to create a good condition for deeper drilling operation. High-density drilling fluid with good precipitation stability and lubricant anti-sloughing properties also contributed to the success in drilling of high pressure brine layer and salt gypsum formation.
Accurate determination of the must-be-blocked point is the key to the success. Drilling of the well with problems and its final solution could be used for a technical reference as drilling in deep or ultra-deep wells in similar geologically complicated oil
and gas fields.
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.
Drilling the hard/abrasive Travis Peak/Hosston and Cotton Valley formations in East Texas/North Louisiana creates a distinctive challenge for polycrystalline diamond compact (PDC) bits. Conventional PDC cutters fail quickly due to abrasive wear/spalling and/or delamination of the diamond table. Most bits are typically pulled in poor dull condition graded 1-2-WT or worse. The situation has caused stagnation in PDC performance and limited additional gains in total footage and rate of penetration (ROP). Recent scientific studies have indicated that thermal fatigue of the diamond table is the main contributing factor leading to cutter failure and is restricting further advancement of PDC drilling in East Texas and other hard and abrasive applications. To improve cutter performance the industry must:
1. Manufacture a cutter to resist abrasive wear and retain a sharp edge for an extended amount of footage
2. Reduce/maintain temperature at the cutter edge to minimize thermal fatigue
To accomplish the objectives, engineers refined and implemented several new processes to increase abrasion resistance and maintain temperature at the cutter tip. This technology platform includes:
1. Enhanced High Temperature/High Pressure (HTHP)sintering process
2. Refined post-pressing process to improve thermal stability
3. Optimized hydraulics to maximizing cutter cooling
In laboratory experiments, the next generation O2 cutter has demonstrated approximately 15% improvement in resistance to abrasive wear compared to the previous generation of premium cutters (O1). Laboratory tests also confirm that optimizing cutter cooling has enhanced the life of the new shearing element. In East Texas field tests, PDC bits equipped with the new cutter and optimized hydraulics have achieved an average ROP increase of approximately 25% while producing improved dull bit condition. These new technologies are expected to have a positive economic impact in the East Texas/North Louisiana Haynesville shale play and in other hard and abrasive applications worldwide.
In the oil industry, there are many situations where fluid flow in annular spaces takes place. During the oil well rotary drilling for instance, the drill bit oscillations change the well cross-section from an expected circular to an elliptic shape. In these cases, the drilling fluid flow through the annular space that is molded between the drill string and the rock formation is a matter of concern so that the correct evaluation of pressure drop and shear stress distribution along the borehole is quite important for an appropriate well design. Despite its importance, studies related to non-Newtonian fluid flow through eccentric or even concentric elliptical annuli are not reported in the open literature. Therefore this paper presents an analytical friction factor correlation for viscoplastic fluid flow through two types of elliptical cross-sectional ducts: a concentric elliptical annulus and an eccentric one. The solution is based on the slot flow model of variable height that is validated comparing the results with the literature and with numerical results obtained from computational fluid dynamics. Very good agreement for the eccentric annular pipe was obtained from the comparison between the current analytical results and the numerical solutions from the literature. A promising application of the present analytical solution for the eccentric elliptical annular duct flow was found when comparing the results with computational fluid dynamics ones.