Description: Publication date: February 2018 Source: Petroleum Exploration and Development, Volume 45, Issue 1 Author(s): Alireza NASIRI, Mohammad Javad AMERI SHAHRABI, Mohammad Amin SHARIF NIK, Hamidreza HEIDARI, Majid VALIZADEH To improve the thermal stability of starch in water-based drilling fluid, monoethanolamine (MEA) was added, and the effect was investigated by laboratory experiment. The experimental results show that the addition of monoethanolamine (MEA) increases the apparent viscosity, plastic viscosity, dynamic shear force, and static shear force of the drilling fluid, and reduces the filtration rate of drilling fluid and thickness of mud cake apparently. By creating hydrogen bonds with starch polymer, the monoethanolamine can prevent hydrolysis of starch at high temperature. Starch, as a natural polymer, is able to improve the rheological properties and reduce filtration of drilling fluid, but it works only below 121 °C. The MEA will increase the thermal stability of starch up to 160 °C. There is a optimum concentration of MEA, when higher than this concentration, its effect declines.

Description: Publication date: December 2017 Source: Petroleum Exploration and Development, Volume 44, Issue 6 Author(s): Gongcheng ZHANG, Wu TANG, Xiaojun XIE, Zhigang ZHAO, Zhao ZHAO Based on the seismic, drilling, cores and outcrops data, the formation of basins, source rocks and hydrocarbon accumulations in the southern South China Sea (SSCS) were systematically analyzed to reveal the petroleum geological features of continental margin basins and summarize the distribution rule of oil and gas in the SSCS. The results show that the South China Sea (SCS) has experienced three tectonic stages, namely, the formation and development of proto-SCS, the subduction of proto-SCS and development of neo-SCS, the rapid subsidence and shrinking of SCS. The tectonic evolution of proto-SCS and neo-SCS controlled the regional tectonic pattern of continental margin in the SSCS, forming southern and northern basin belts, and also dominated the formation of basins, source rocks and hydrocarbon accumulation characteristics. The source rocks were mainly Miocene coal source rocks in the southern basin belt, with different thermal evolution degree, and the near-shore source rock was chiefly oil-generating while the off-shore source rock was mainly gas-generating. Compressive folding structural belts and reefs were the favorable belts. Within the northern basin belt, the source rocks were gas-prone and dominated by the Eocene to Oligocene, with high thermal evolution degree. Reefs and faulted blocks were the major accumulation areas. Our study demonstrates that the continental marginal basins of SSCS still have great exploration potential and is an important strategic area of oil and gas exploration and development. The southern basin belt focuses on oil and gas exploration and the northern basin belt focuses on gas exploration.

Description: Publication date: December 2017 Source: Petroleum Exploration and Development, Volume 44, Issue 6 Author(s): Shuxin PAN, Huaqing LIU, Carlos ZAVALA, Caiyan LIU, Sujuan LIANG, Qingshi ZHANG, Zhongfeng BAI Based on the integrated analysis of seismic, drilling and core data, a large channel-fan system of hyperpycnal flow origin was found in the Qijia-Gulong area of the Nen 1 Member of the Cretaceous Nenjiang Formation in the Songliao Basin. The hyperpycnal flow in this area, which originated from the edge of the basin and then passed the northern delta, formed a complete channel-fan system in the deepwater area. The channel-fan system comprises straight channels and meandering channels extending from north to south over a straight distance of more than 80 km with a width of 100−900 m, and distal fan lobes at the channel tip cover a maximum area of 20 km 2 . This system, which is dominated by fine-grained deposits, contains massive sandstone, sedimentary structures of flow-water origin, and internal erosion surfaces; it also contains abundant continental organic clasts and exhibits evidence of bed-load and suspended-load transportation mechanisms. The hyperpycnite sequence contains pairs of coarsening-upward lower sequences and fining-upward upper sequences, reflecting the dynamic features of cycles in which floods first strengthen and then weaken. A new sedimentary model has been built for hyperpycnites in the Songliao Basin.

Description: Publication date: December 2017 Source: Petroleum Exploration and Development, Volume 44, Issue 6 Author(s): Chao WANG, Yanfang LYU, Quan WANG, Guang FU, Yougong WANG, Yonghe SUN, Zhipeng HUO, Junqiao LIU To study the possibility and location of lateral migration of oil and gas across faults, a quantitative evaluation method for lateral migration of oil and gas across faults was established using the Shuangjing Knipe graphic method to identify the juxtaposition site and juxtaposition patterns of sand and sand in the upper and lower walls of the reverse faults and the consequent faults, combined with the oil and gas limit method of fault lateral seal in the test oil area. The quantitative evaluation method was applied to the first and two members of the Paleogene Shahejie strata (referred to as Es1 and Es2) of Shigezhuang nose structure of Wen'an slope in Baxian sag, Jizhong depression, Bohai Bay Basin, to determine the juxtaposition site of sand and sand in the upper and lower walls of the fault, and the shale gouge ratio (SGR) lower values are 26% and 29% respectively in the strata Es1 and Es2. Thus, the location of lateral migration of oil and gas across faults was determined. Based on the oil and gas distribution characteristics of the strata Es1 and Es2, and variation trend of nitrogen compounds in 4 wells in the strata Es1, the results were consistent with the quantitative evaluation of the location of lateral migration of oil and gas across faults, the feasibility of the evaluation method was preliminarily verified.

Description: Publication date: December 2017 Source: Petroleum Exploration and Development, Volume 44, Issue 6 Author(s): Tao MENG, Peng LIU, Longwei QIU, Yongshi WANG, Yali LIU, Hongmei LIN, Fuqi CHENG, Changsheng QU The upper part of the 4th member of Paleogene Shahejie Formation in Bonan sag, Bohai Bay Basin, East China was taken as the study object. Conventional core analysis, casting and conventional thin section inspection, scanning electron microscope observation, particle size analysis and fluid inclusion analysis were carried out on cores, and the data from these analyses and tests was used to find out the evolution of diagenetic environment of the saline lacustrine basin and the main factors controlling the deep formation of high quality reservoirs. The diagenetic environment of the saline lacustrine basin experienced alkali and acid alternation. In the early alkali diagenetic environment, large amounts of carbonate cement filled the primary pores, making the reservoir porosity reduce sharply from 37.3% to 18.77%, meanwhile, keeping the primary pores from compaction, and retaining the dissolution space. In the middle-late stage of acid diagenetic environment, early carbonate cement was dissolved, resulting in rise of reservoir porosity by 10.59%, and thus the formation of the deep high quality reservoirs. The distribution of high quality deep reservoirs is controlled by the development of gypsum salt rock, source rock, fracture system and sedimentary body distribution jointly. Deeply buried high quality reservoirs in the upper part of the 4th member of the Shahejie Formation in Bonan sag are nearshore subaqueous fan-end sandstone and some fan-medium fine conglomerate buried at 3 400−4 400 m in the north steep slope.

Description: Publication date: December 2017 Source: Petroleum Exploration and Development, Volume 44, Issue 6 Author(s): Yong WU, Lu ZHOU, Feiyan ZHONG, Kexiu ZHONG, Bing YUAN, Jieling ZHOU Based on the slope theory in geomorphology, a method, which can identify the boundary of platform reef by high precision slope attribute calculation based on the horizon data of fine seismic interpretation, combining the ancient geomorphic analysis method, was established. The conventional seismic prediction methods, drilling results and the thickness data of Changxing Formation were used to verify and supplement this method. Then, this method was used to identify the boundary of uplifted reef on the planar image in the Permian Changxing Formation in Luodingzhai area of Sichuan Basin. The results show that the reef boundary imaged by this method is consistent with the reef distribution revealed by the drilling, and is clearer in local details. Compared with conventional seismic prediction methods, the reef boundary identified based on the same fine seismic horizon interpretation results by this method has no multiple solution on the planar image.

Description: Publication date: October 2017 Source: Petroleum Exploration and Development, Volume 44, Issue 5 Author(s): Yunfeng ZHANG, Fei TAN, Haizhou QU, Zhiqi ZHONG, Yong LIU, Xinsheng LUO, Zhenyu WANG, Fang QU Abstract Based on the fine characterization of weathering crust paleokarst landform of the Ordovician Yingshan Formation in Lungu area, Tarim Basin, the size, number and reservoir controlling characteristics of karst monadnocks have been investigated quantitatively. Impression method and karst monadnock volume formulas were employed to characterize the various levels of karst microtopography, to work out the number, relative relief, area, volume and other parameters of monadnocks, and analyze the reservoir development situation at different parts of monadnock. The results showed that the weathering crust karst reservoirs in Lungu area are 140-160 m in relative altitude, and thinning from karst highland to karst slope and terrace. Two hundred fifty-two karst monadnocks have been identified in the study area. Among them, type I and type II monadnocks are fewer in number, but larger in bulk volume, and are favorable reservoir development zone. The karst monadnocks have a high coincidence ratio with current structural high points of 96.42%, and the monadnock morphology has remained basically unchanged during the late tectonic movement, thus “karstification-reservoir-accumulation” configuration has been kept good. In the main part (core) of karst monadnocks, there are cave, vug, fracture-vug, and fracture reservoirs, thicker high quality reservoir, and all reservoir parameters are better than those of karst monadnock wings. It is found that the relative amplitude of karst monadnock is positively correlated with single well productivity, and the scale and position of monadnock are closely related with productivity.

Description: Publication date: October 2017 Source: Petroleum Exploration and Development, Volume 44, Issue 5 Author(s): Wenlong GUAN, Changfeng XI, Long CHEN, Muhetar, Chengguo GAO, Junshi TANG, Qiu LI Abstract The targets, strategies and approaches of the field controlling processes of combustion assisted gravity drainage (CAGD) are discussed based on the research of its mechanisms, advantages and defects. By taking fully advantage of gravity, CAGD process can produce the mobilized oil near the combustion front through the underlying horizontal well, serving as a possible solution for extra-heavy oil production in Xinjiang oil field. However, unidirectional conning and breakthrough of combustion front are risky to happen during the field application of CAGD. Based on laboratory three-dimensional physical simulation experiments and the experience of former pilots, it is proposed that a gently upward sloping combustion front is beneficial for the steady drainage of mobilized oil and should be the target of CAGD control. Key production parameters like the maximum production rate and corresponding air injection rate during field application are calculated with reservoir engineering approach and material balance theory. The maximum oil production rate of the CAGD pilot in Block Fengcheng, Xinjiang oil field, is 12.9 m 3 /d, and the air injection rate is 14 048 m 3 /d. To maximize the oil productivity and sustain combustion front moving forward steadily, the ignition position should be located at the mid-upper parts of the formation; the air injection rate at the early stage should keep slow and increase gradually; meanwhile, the production rate of flue gas should be 90% of the air injection rate. A pilot of CAGD was initiated in the Xinjiang Fengcheng Field on the basis of those research outcomes. By the end of 2016, Well Group FH005 in the pilot has succeeded in steady production for more than 400 days. Key aspects, involving the shape of combustion chamber, oil production of single horizontal producer, air oil ratio and the degree of oil upgrading are in accordance with what the development plan predicted.

Description: Publication date: October 2017 Source: Petroleum Exploration and Development, Volume 44, Issue 5 Author(s): Jie CHI, Binshan JU, Guangzhong LYU, Xing ZHANG, Jiabei WANG Abstract Based on the theory of non-Darcy seepage, a mathematical model for CO 2 miscible and immiscible concurrent flooding considering changes of oil viscosity and threshold pressure gradient of oil and CO 2 is established. A computational method of critical well spacing of CO 2 miscible and immiscible concurrent flooding in ultra-low permeability reservoirs is deduced by solving the distribution of CO 2 concentration in miscible flooding area with the mass transfer-diffusion-absorption equation and solving the saturation equation of immiscible affected area with characteristic line method. A critical well spacing example is built in the F142 and G89 reservoir blocks and the results show: (1) The critical well spacing increases with gas injection pressure, while decreases with gas injection speed; (2) The contribution of length in pure CO 2 seepage area to the critical well spacing is the largest, the contribution of length in CO 2 -Oil effective mass transfer area and immiscible affected area is secondary, the contribution of pure oil area is the least, the gap of length between pure CO 2 seepage area and CO 2 -Oil effective mass transfer area and immiscible affected area decreases with gas injection speed and it increases with the decreasing of gas injection speed, meanwhile, the law is more significant; (3) Pressure drop gradient of miscible affected area is significantly different from that of immiscible affected area and pressure drop gradient of CO 2 -Oil effective mass transfer area in miscible affected area is bigger than that of immiscible affected area.

Description: Publication date: October 2017 Source: Petroleum Exploration and Development, Volume 44, Issue 5 Author(s): Dmitry Anatolievich NOVIKOV Abstract The available hydrogeochemical data collected over the past four decades in Siberian Arctic areas were analyzed and interpreted comprehensively for the first time, through data ranking, evaluation and analysis, systematic estimation of region, altitude background and abnormal value, and calculation of element molar ratio, different kinds of correlation coefficients in water proximity were estimated. Paleohygdrogeological reconstructions of the Siberian sedimentary basins suggest the presence of three water genetic types in petroleum deposits: (1) Waters that formed during marine sedimentation, (2) Waters of meteoric origin that infiltrated the basin and were involved in supergene processes in the geological past, (3) Waters produced by condensation from a hydrocarbon mixture. Hydrogeochemical patterns of petroleum deposits are controlled by the long geological evolution in the water-rock-gas-organic matter system. Sodium-chloride bicarbonate, sodium chloride, calcium chloride groundwaters, and other types of brines with the total salinity of 0.2-350 g/L are distributed in the Siberian Arctic sedimentary basins. Comparative analysis of groundwaters and brines in the Siberian Arctic revealed a group of sodium chloride water samples had a total salinity of over 250 g/L, suggesting the formation of the brine was related to leaching of evaporite rock. Hydrogeochemical data indicate that composition of the brine has varied dramatically with their evolution. Mesozoic groundwaters and brines of Anabar-Laptev basin and West Siberia existed only in the beginning of their chemical evolution.