ABSTRACTS AND KEY WORDS

SEDIMENTARY FACIES OF SHAHEZI FORMATION IN JINSHAN GASFIELD, LISHU FAULT DEPRESSION, SONGLIAO BASIN

ZHANG Guangquan, LV Lin, SUN Bing, JIA Yuewei, GUO Yandong and FENG Qiong （Sinopec Exploration & Production Research Institute）.NATURALGASEXPLORATION&DEVELOPMENT. v. 39 no.1, pp.1-5，1/25/2016



ABSTRACTS AND KEY WORDS

SEDIMENTARY FACIES OF SHAHEZI FORMATION IN JINSHAN GASFIELD, LISHU FAULT DEPRESSION, SONGLIAO BASIN

ZHANG Guangquan, LV Lin, SUN Bing, JIA Yuewei, GUO Yandong and FENG Qiong （Sinopec Exploration & Production Research Institute）.NATURALGASEXPLORATION&DEVELOPMENT. v. 39 no.1, pp.1-5，1/25/2016

ABSTRACT：In Jinshan oilfield, the reservoir lithology and depositional environment are very complex. A series of studies on geologic mud logging, and well-logging observation, description, and interpretation were carried on. Moreover, for the main bed of Shihezi Formation, its lithological association, sedimentary structure, profile structure, and logging facies association were explored. Results show that（1）during the deposition of Shahezi Formation, one dispositional system of underwater fan was developed at the steep slope belt whereas another system of fan delta was developed at the gentle slope belt, individually；（2）both gravel bar and braided channel are the most favorable sedimentary facies belts；（3）longitudinally, the main channel deposits are more developed gradually from Shahezi 4 and Shahezi 3 members to Shahezi 2 Member, further to Shahezi 1 Member；and（4）the channel swings from east to west. In addition, a depositional mode on Shahezi Formation is mapped out on the basis of comprehensive geological study. Widely developed in the whole Sichuan Basin, the Cambrian Xixiangchi Formation is characterized by large thickness and composed of single lithology (mainly light grey to dark grey thin dolomites interbedded with sandy or argillaceous dolomites). In the past, this formationbook=2,ebook=7with hundreds of meters in thickness was always studied as a single geologic unit. So, in order to deepen its study, both rock type and lithologic association of the Xixiangchi Formation were analyzed for more than ten exploration wells in central Sichuan Basin. Moreover, its substrata were divided and sedimentary facies was explored. Results show that（1）platform plate deposits were developed mainly in both Xixiangchi 1 and Xixiangchi 3 stages whereas lagoon deposits were developed in Xixiangchi 2 stage; and（2）the slope belt in paleo-uplift block is a favorable exploration block due to wide distribution and large thickness of grain shoal in both Xixiangchi 2 and Xixiangchi 3 stages. Based on some seismic and geologic data on Fuling area, Sichuan Basin, the tectonic evolution features since Indosinian period and its effect on oil and gas accumulation are systematically analyzed. It’s deemed that in this area,（1）the structure appeared a saddle feature of high in south-north part and low in central part caused by its uplift from Indosinian to early Yanshanian period; and（2）a compaction began from late Yanshanian period, however the most active compaction occurred during Himalayanian period. In addition, integrating with a study on sedimentary burial history, we consider that oil and gas reservoirs, which are generated by marine source-reservoir-caprock association, are affected by tectonism. and The reservoir forming experienced three processes, including paleo-reservoir forming from Indosinian to early Yanshanian period, paleo-reservoir developing in middle to late Yanshanian period, and reservoir reforming in Himalayanian period. Tectonism has various effects on different sequences or trap types. The shale of Lower Cambrian Qiongzhusi Formation in eastern Yunnan Province, a marine sedimentary stratum in South China, is characterized by wide distribution, large thickness, high organic-matter abundance, and most in high- to overmature evolution degree. Furthermore, its organic matter mainly contains type-I kerogen with a strong gas-generating capability. Its physical property is good due to high content of brittle mineral. It is found that there is a clear gas logging abnormality during a drilling. Gas content is an important parameter to evaluate gasbearing property. In this study, based on some data from geology and experiments on shale of Qiongzhusi Formation, the gas-bearing property and its controlling factors were analyzed. Resultsbook=4,ebook=9show that（1）there is a positive correlation existing among gas content with organic-matter abundance, porosity, and burial depth whereas no obviously correlation with organic-matter maturity; （2）gas can be also found from both sandstones and carbonates in this formation; and（3）this Qiongzhusi Formation has an exploration potential of shale gas. Memory well-logging equipment is self-developed by Well Logging Company, CNPC Chuanqing Drilling Engineering Company Limited. In this study, its application to shale formations was analyzed, and data from both wireline logging and logging while drilling（LWD）was compared. Moreover, not only logging quality but also evaluation methods were explored. Results show that（1）this equipment is available for complex shale formations; and（2）better quality can be obtained from natural gamma ray, resisitivity, and acoustic logging to meet a demand of reservoir evaluation. In addition, some memory logging information can be used to evaluate shale-gas reservoirs and to optimize testing intervals. The measured results demonstrate that the well-logging information is reliable. During a seismic survey in mountains, a surface investigation is very important and its accuracy can influence on the validity of both well-depth design and static correction, further affecting the quality of seismic profile. So, with higher accuracy, such microlog methods as shooting in hole and receiving at surface should be used in mountains. Taking a 2D seismic survey in Xingcheng as an example, we analyzed some technological difficulties existing in these methodsbook=5,ebook=10and made many flexible measures. A better result has been obtained after their application. In a small fault-depression basin, the fault depressions are the main exploration targets in northern Songliao Basin. But their SNR is often low, resulting in poor imaging effect. So, an experiment on high-density wide line was carried out. Based on these wide line data, the effects of different covering times and shot-trace densities on noise energy and effective reflection energy were studied by a degradation analysis with a wavefield separation method. Results show that the effects of different covering times are various. In addition, an effective wide line observation system forms on the basis of the shot-trace density, and it can increase the imaging effect for these fault depressions. The existence of starting pressure gradient was confirmed by laboratory test in Xujiahe 2 reservoir of Hechuan gasfield, which is featured by low permeability and high water cut. The flow field, supply radius, and recovery ratio of gas well were studied by using seepage mechanics and single-well numerical simulation. Results show that（1）this gradient narrows supply area and produces pressure drop, causing a rapid falling of flow pressure and forming a coneshaped pressure-drop profile;（2）the recovery ratio decreases with an increase of well spacing, and the reserves can not be used outside the limit supply radius. Based on the principle of similitude, a new method to estimate this supply radius, recoverable reserves, and recovery ratio has been estab-book=6,ebook=11lished for low-permeability gas reservoirs. It’s a simple method taking the influences of starting pressure gradient, the lowest（abandoned）pressure, and well spacing into consideration. Its application results are consistent with actual dynamic monitoring and drilling data, which shows its validity. It’s very significant to determine economical well spacing and further develop low-permeability gas reservoirs. Penglaizhen Formation, Ma-Shi-Guang area, is a typical tight sandstone gas reservoir with atmospheric-high pressure, and is characterized by strong heterogeneity. There exists great variance in gas output after fracturing. In some wells, a testing production after fracturing is low but increases significantly after producing or shut in for some time. Given this, some reservoir properties were analyzed. Results show that these wells with production increase are characterized by high shale content in reservoir, and their porosity and permeability are higher than the averages of this area. According to microscopic characteristics and percolation mechanism, we consider that the main factors causing this production variance are water sensitivity and waterphase trapping damage. Furthermore, a fracturing technology to reduce water sensitivity and damage is proposed. As a stimulation treatment, volume fracturing is very necessary for shale-gas reservoirs. How to evaluate its effect is an urgent problem. Based on productivity evaluation, anal-book=7,ebook=12ysis on multifactor influencing fracturing effect, and correlation and multiple-regression analysis, the evaluation indicators of fracturing effect and fracturing technology are established. The impact of fracture geometric parameters on fracturing has been defined by theoretical calculation. Through the index of productivity changes of fractured wells, an evaluation method formes, in which the after-fracturing production performance is taken into account. And the fuzzy mathematics is applied to calculating evaluation indicators to solve some contradictions between geological and engineering factors. Results show that data support system can meet the requirement of effect evaluation of shale-gas volume fracturing. Meanwhile, significant economic benefits may be obtained. Due to poor fracture development and low permeability, most tight gas reservoirs are usually exploited by horizontal drilling combined with fracturing stimulation. Research shows that, in these reservoirs, there exists generally stress effect, starting pressure, and even gas-water two-phase flow. At present, reports about the productivity solution model for gas-water two-phase flow are very seldom. Based on a conventional fractured horizontal well model of open-hole completion, considering the stress sensitivity, starting pressure gradient, and mutual interference among fractures, we define the gas-water two-phase pseudo pressure. And through the superposition principle of potential and the law of equivalent percolation resistance, a gas-water two-phase steady-state productivity model is derived, which provides a new method for productivity solution. Case study indicates that（1）productivity increases gradually with increasing permeability modulus and fracture percolation rate;（2）productivity decreases with an increase of water-gas volume ratio; and（3）starting pressure gradient has no obvious effect on productivity. Therefore, during a development of tight gas reservoirs, it is necessary to optimize fracture parameters to reduce the impact of gas-water two-phase flow on productivity. As a new stimulation and completion technology, hydraulic jetting radial perforation can improve a percolation environment within reservoirs, break through a near-bore pollution zone, connect undeveloped reservoirs far away wells with wellbore, enlarge a drainage area, and finally improve development effect. With some characteristics of poor physical properties, low permeability, undeveloped fractures, high water saturation, and strong heterogeneity, the gas reservoir of Penglaizhen Formation, Baimamiao gasfield, is hard to be developed. A pilot production started from 2001, and now its development is in the mid to late stage with the recovery ratio of 5.6% only. To enhance this recovery, some technologies including foam drainage, supercharger, and plunger gas lift were adopted. However, these technologies can not improve reservoir conditions and enlarge seepage area fundamentally. Thus, a technology of hydraulic jetting radial perforation is applied. And its application conditions for Penglaizhen gas reservoir are evaluated. Therefore, this technology may be popularized for shallow gas reservoirs of Baimamiao area. Pore-, collapse-, and fracture-pressure profile (also called three-pressure profile) is the foundation to optimize a casing-program design and to determine a safe drilling-fluid density window. This three-pressure profile calculated by logging methods is combined with field pressure data to establish a three-pressure profile of GM block. Based on its characteristics, thebook=9,ebook=14casing-program optimization and the safe density window determination are carried out. Results show that drilling of Xujiahe 2 Member of target layer qualifies for three hole-in casing program optimization. And it is unreasonable to determine drilling-fluid density according to pore pressure. For one section from J3p to T3x5, micro-ultra collapse pressure is recommended; and for T3x4section, micro-ultra pore pressure is recommended, respectively. The study provides a scientific basis for drilling design and site operation. Field application also indicates that the drilling efficiency has been improved and the drilling cost may be reduced, resulting in better economic benefits. Chaluhe reservoir of Yitong Basin is a low-porosity and -permeability one with effective porosity of 8.4%～14.7% and permeability of 0.3～8.9 mD. Some abnormality often appears during its fracturing. The reservoir characteristics of sandstone interbedded with mudstone, hardness, and densification, combining with formation damage caused by slurry filtration, all can lead to some problems including abnormally high pressure, fracturing failure, and sand adding difficulty. So, according to lithology and pollution characteristics, a high -strength compound acid-fluid system and additives are optimized. The corrosion ratio of this acid-fluid system to both rock samples and drilling slurry is higher than 40% and 28%, respectively. Acidizing reconstruction can change micropore structure of sandstone, increase permeability, and reduce effectively fracturing pressure. A pilot test was carried out. As a result, fracturing pressure fell by 20% after acidification. This study provides technical guarantee for further development. Lianhuashan structure is situated at the frontal depression of Longmenshan overthrust nappe belt, western edge of Sichuan Basin. Some thrust faults are developed in this complex structure. Above the directional point, Jiaguan Formation is dominated by sandstone interbedded with mudstone featured by weak cementation. Serious lost circulation and no-return problems may occur while drilling. Under the directional point, Xujiahe 5 Member consists of shale interbedded with sandstone, and mixed with carbonaceous shale and coal bed. Due to large dip angle, formation collapse may occur frequently. Therefore, a methodology of safety drilling for directional well is developed according to the research on drilling parameter, bit and drilling-fluid system optimizations, plugging measures, electronic logging, and casing running. Field test shows that the methodology is obviously effective. Along with a large-scale development of Jinbian gas storage, Changqing oilfield, there are more and more difficulties occurring in a drilling, further affecting severely its operation. So, some key technologies have been developed, including well trajectory control, sidetracking with Φ311.2 mm wellbore, drilling carbonaceous mudstones in a coal seam, borehole cleaning, horizontal-section drilling with Φ215.9 mm wellbore. These technologies can provide a certain foundation for a sustainable development of Jinbian gas storage. As a novel natural-gas mineral in China, shale gas has a broad prospect for exploitation. Shale-gas reservoirs are characterized by low porosity and permeability, further resulting in a demand to high cementing quality. However, their geological characteristics, drilling and completion methods, and development modes may decide that it’s more difficult to implement a cementing in shale-gas wells than that in conventional gas wells. Based on a lot of features of shale-gas resources in China, many cementing difficulties were analyzed in terms of displacement efficiency, cement-sheath integrity, and cement slurry selection. Results show that the main challenges include horizontal-well cementing with irregular borehole, ensuring the cement-sheath integrity for a long time, and keeping a balance between cement-slurry property and cost. In addition, three suggestions are made to increase exploration and development benefits for shale-gas wells, containing（1）to increase displacement efficiency under complicating well conditions,（2）to carry out an evaluation on long-term cement-sheath integrity, and（3）to develop a cement-slurry system. TS2 well, located at Kuche area in Tahe oilfield, is a risk-exploration one deployed by Sinopec Northwest Company. It is also situated at a leakage block with low pressure. Without reference to cementing in this block, however during this cementing, we analyzed difficulties, made measures, optimized slurry system, increased PVF based on particle sizing theory, used some advanced light weight material abroad, and developed a slurry with extra-low density of 1.25g/cm3. As a result, the whole cementing process is smooth and good quality rate reaches 82.32%.

KEY WORDS:
SUBSTRATA DIVISION AND SEDIMENTARY EVOLUTION OF XIXIANGCHI FORMATION, CENTRAL SICHUAN BASIN
CHEN Wen, LIU Xin and ZENG Yiyang（Exploration and Development Research Institute, PetroChina Southwest Oil and Gasfield Company）.NATURAL GAS EXPLORATION &DEVELOPMENT. v. 39 no.1, pp.6-8，1/25/2016Lishu Fault Depression, Jinshan oilfield, Shahezi Formation, fan deltaic deposition, braided channel central Sichuan Basin, Xixiangchi Formation, substrata division, grain shoal, sedimentary evolution Fuling area, tectonic evolution, reservoir forming Sichuan Basin, western margin of Luzhou Paleohigh, T2l11, reservoir forming, favorable exploration block eastern Yunnan Province, Cambrian, Qiongzhusi Formation, shale gas, gasbearing property shale, memory well logging, reservoir evaluation, logging efficiency shooting in hole, microlog, mountains, sidewall protection, water shooting high-density wide line, fault depression, shot-trace density, degradation analysis starting pressure gradient, low-permeability gas reservoir, pressure-drop profile, supply radius, recovery ratio, economical well spacing production increase, water sensitivity, water saturation, thickness of liquid film, water-phase trapping shale gas, volume fracturing, database, system, effect evaluation tight gas, fracturing, horizontal well, gas-water two phase, productivity hydraulic jetting radial perforation, Penglaizhen gas reservoir, Baimamiao gasfield, application condition pore pressure, collapse pressure, fracture pressure, casing program, safe drilling-fluid density abnormal fracturing, fracture pressure, acidification, field application Lianhuashan structure, directional well, safety, drilling technology sidetracking in a gas storage, carbonaceous mudstones, reduction of friction and drag against fish, reaming, finding out original borehole shale gas, cementing, displacement, cement-sheath integrity, cement slurry extra-low density, slurry, leakage well, cement

PETROLEUM GEOLOGICAL CONDITIONS OF T2L11, WESTERN MARGIN OF LUZHOU PALEOHIGH, SICHUAN BASIN

ZHAO Xin1, CHEN Wen2, WANG Hua2, YANG Yuran2and LIN Zhixin3（1. Chengdu University of Technology; 2. Exploration and Development Research Institute, PetroChina Southwest Oil and Gasfield Company; 3. Southwest Petroleum University）.NATURAL GAS EXPLORATION & DEVELOPMENT. v. 39 no.1, pp.14-16，1/25/2016

ABSTRACT：In Sichuan Basin, a lower rate of the proven gas resources is reported from the Leikoupo 1 Member（T2l11）. Except some T2l11gas reservoirs in both Wolonghe gasfield（in eastern basin）and Moxi gasfield（in central basin）, no large-scale reserves have been obtained from this member in the rest of basin. So, there are large amount of remaining resources with a bright exploration prospect. The T2l11in the western margin of Luzhou Paleohigh, which belongs to a deposition of grain shoal facies, experienced dolomitization of compound water and dissolution to form a lot of intercrystalline and intergranular dissolved pores. Moreover, during T2l11stage of the end of middle Triassic, the shoal-facies deposits experienced epigenetic dissolution to form some high-quality reservoirs; further this T2l11reservoir contacted directly with the overlying source rock of Xujiahe Formation , which is available for a lateral migration. In this area, well developed faults and fractures connecting Permian sources with Upper Triassic sources, are the main migration pathway. Plenty of traps with large area and high closure are conducive to oil and gas accumulation.

APPLICATION OF HYDRAULIC JETTING RADIAL PERFORATION TO PENGLAIZHEN FORMATION, BAIMAMIAO GASFIELD

YANG Yuanyu2, WANG Jun1, CHENG Fangmin1, LIU Bo1, WANG Xian1and ZHANG Wenjuan1（1. Northwestern Sichuan Gas District, PetroChina Southwest Oil and Gasfield Company; 2. Chengdu University of Technology）.NATURAL GAS EXPLORATION&DEVELOPMENT. v. 39 no.1, pp.52-56，1/25/2016

SAFETY DRILLING TECHNOLOGY FOR DIRECTIONAL WELL OF LIANHUASHAN STRUCTURE

YANG Yongwen, WANG Cailing, YANG Jiechao, PENG Kuanjun and GUO Lite（Chuanxi Drilling Company, CNPC Chuanqing Drilling Engineering Company Limited）.NATURAL GAS EXPLORATION&DEVELOPMENT. v. 39 no.1, pp.63-64，1/25/2016

PRACTICE IN REAMING AGAINST FISH

ZHANG Jie, HE Wenping, CHANG Zhongyong and DENG Hui（Chuandong Drilling Company, CNPC Chuanqing Drilling Engineering Company Limited）.NATURAL GAS EXPLORATION &DEVELOPMENT. v. 39 no.1, pp.70-73，1/25/2016

ABSTRACT：Gas storage is a strategic and livelihood project in national energy building. However, the success or failure of some subsurface construction including drilling and workover directly threats an establishment of whole gas storage. Moreover, whether an effective control and blocking to a drilled reservoir or not is the key for its construction. In this paper, a method, called reaming against fish, is presented. During a drilling, after a fishing fish can be implemented because of some sticking accidents, this method may be used to make wellbore went over this fish section and to keep smooth. As a result, reservoir can be controlled effectively. Pioneered in domestic drilling industry, this method as an innovation technology can solve sticking accidents, and its application can also lay the foundation of gas-storage construction.

CEMENTING WITH EXTRA-LOW DENSITY SLURRY IN TS2 WELL

NING Heqing（Cementing Company, Sinopec Group Southwest Oil & Gas Company）.NATURALGASEXPLORATION&DEVELOPMENT. v. 39 no.1, pp.77-79，1/25/2016

翻译何颋婷刘婕

审校刘婕

编辑王晓清