A quantitative evaluation for well pattern adaptability in ultra-low permeability oil reservoirs:A case study of Triassic Chang 6 and Chang 8 reservoirs in Ordos Basin

Based on the previous studies and development practice in recent 10 years, a quantitative evaluation method for the adaptability of well patterns to ultra-low permeability reservoirs was established using cluster analysis and gray correlation method, and it includes 10 evaluation parameters in the four aspects of optimal evaluation parameters, determination of weights for evaluation parameters, development stage division, and determination of classification coefficients. This evaluation method was used to evaluate the well pattern adaptability of 13 main ultra-low permeability reservoirs in Triassic Chang 6 and Chang 8 of Ordos Basin. Three basic understandings were obtained: Firstly, the well pattern for ultra-low permeability type-I reservoirs has generally good adaptability, with proper well pattern forms and well pattern parameters. Secondly, square inverted nine-spot well pattern is suitable for reservoirs with no fractures; rhombic inverted nine-spot injection pattern is suitable for reservoirs with some fractures; and rectangular well pattern is suitable for reservoirs with rich fractures. Thirdly, for the ultra-low permeability type-Ⅱ and type-Ⅲ reservoirs, with the principles of well pattern form determination, the row spacing needs to be optimized further to improve the level of development of such reservoirs.

Land Use of the Three Gorges Reservoir Area and the Effect on Its Landscape Pattern in the Recent 50 Years

The paper makes detailed analysis on the changing processes of the main types of land use in Three Gorges Reservoir Area through the techniques of RS （Remote Sense） and GIS （Geography Information System）. Based on the theory of landscape ecology, many types of landscape pattern indexes are calculated and made correlation analysis. The results indicate that： in 1995 the ecological environment of Three Gorges Reservoir Area was the most vulnerable in the recent 50 years, but resumed in 2002; the landscape pattern diversity index, fractal dimension index and fragmentation index has close correlation with the area of land use/cover change （LUCC）. The research also releases that the increase of the cultivated land, grassland and construction land deteriorates the landscape ecological pattern, while the increase of forest land area will help restore the landscape ecological pattern to its original state. The rapid change of grassland is an important index of the change of landscape pattern, because it has the most effect on change of landscape pattern index.

Distribution Patterns of Remaining Hydrocarbons Controlled by Reservoir Architecture of Distributary Channel with Different Channel Style: S2 Formation of Songliao Basin, China

1 Introduction Reservoir architecture analysis of distributary channel of Daqing oilfield has drawn consistent interest among development geologists and petroleum engineers over the last decade(Lv et al.,1999;Zhou et al.,2008;Zhang et

Analysis of Landscape Patterns and the Trend of Forest Resources in the Three Gorges Reservoir Area

In this paper, first, based on landscape ecology theories, we respectively selected indexes from 4 aspects, area, edge, shape, and density, of the landscape type to describe the status of forest landscape patterns, and we established the stability index of landscape pattern (LSBI). Then, based on geo-statistical theories, we divided the forest in the reservoir area into 3990 grids of 4 km × 4 km using network technology and employing ordinary Kriging modelling to make trend surface analyses of the forest resources in the reservoir area. Finally, based on statistics principles, we used sampling theory to systematically extract 227 samples to obtain 7 periods of remote-sensing data from 1990a to 2012a. Then, we classified and extracted the forest in the sampling area using remote sensing, and we analysed each result with an Autoregressive Integrated Moving Average Model (ARIMA) time-series model. The results indicated the following: 1) the landscape structure of the reservoir area was primarily needle-leaved forest, broad-leaved forest and bush forest, and the mixed stands and bamboo stands were secondary;2) the difference of the forest landscape pattern stability in the reservoir area, in all directions, was not significant, but the southern region was slightly more stable;and 3) the stability of the forest landscape pattern in the reservoir area increased from 1990a to 2012a. It kept increasing until 2016a. This study provides a theoretical basis for the reasonable management and decisions about the forest resources in the Three Gorges Reservoir Area. Meanwhile, it also explores methods for relevant research and has practical significance.

Exploiting pattern and sustainable development of marginal lands in the Three Gorge Reservoir Areas

This paper studied the distribution and utilization status, reasonable exploitation patterns and potential productivity, and sustainable development of marginal lands in the Three Gorge Reservoir Areas. It has been pointed that problems of the soil fertility degradation, poor productivity in crop lands, natural disasters and environmental deterioration existed in all the exploited marginal lands. In order to maintain the sustainability of the marginal lands, following measure have been proposed: prohibiting cultivation in the crop lands with a slope more than 25°, restoring vegetation in the slope more than 25°, strengthening the basic agricultural construction, establishing the production base of woody feeds and oils, establishing a multi dimensional management model with reasonable structure and optimum function for forestry, agriculture and fishing.

The Characteristics of Soil Nutrients in Terracing Land under Different Land Use Patterns in Three Gorges Reservoir Area

In this study,taking the typical terracing land in Wushan County of Chongqing Municipality for example,we study the distribution of soil nutrients in the terracing land under different land use patterns in Three Gorges Reservoir Area. We conduct field survey and sampling on three different land use patterns( cash crop land,food crop land and abandoned land),and do the indoor experimental analysis of soil nutrient indicators. The results indicate that there is significant or very significant impact on soil nutrients under different land use patterns. The content of soil organic matter declines in sequence from abandoned land,food crop land to cash crop land; the content of soil N declines in sequence from cash crop land,abandoned land to food crop land; the content of soil P declines in sequence from cash crop land,food crop land to abandoned land; the content of soil K declines in sequence from abandoned land,cash crop land to food crop land. The result is in close relation to land use patterns,human cultivation activity,land disturbance and application of fertilizer.

Experiments on the influences of well pattern on water flooding characteristics of dissolution vug-cave reservoir

Based on the similarity criterion, volcanic rock samples were taken from outcrops to make experimental models. Water flooding experiments of five-spot well pattern, nine-spot well pattern, five-spot to nine-spot well pattern, the relationship between relative well and fracture positions, and injection rate in dissolution vug-cave reservoirs with/without fractures were carried out to analyze variation regularities of development indexes, find out development characteristics of water flooding with different well patterns and sort out the optimal water flooding development mode. For dissolution vug-cave reservoirs without fractures, five-spot well pattern waterflooding has very small sweeping area, serious water channeling and low oil recovery. When the well pattern was adjusted from five-spot to nine-spot well pattern, oil recovery could be largely improved, but the corner well far from the injector is little affected. In dissolution vug-cave reservoirs with fractures, when the injector and producer are not connected by fractures, the fractures could effectively connect the poorly linked vugs to improve the development effect of water flooding. Whether there are fractures or not in dissolution vug-cave reservoirs, the development effect of nine-spot well-pattern is much better than that of five-spot well pattern and five-spot to nine-spot well pattern, this is more evident when there are fractures, and the edge well has better development indexes than corner well. At the high-water cut stage of water flooding with nine-spot well pattern, the oil recovery can be further improved with staggered line-drive pattern by converting the corner well into injection well. It is helpful to increase the oil production of corner well of nine-spot well pattern by increasing the injection rate, and improve ultimate oil recovery, but the water-free production period would be greatly shortened and water-free recovery would decrease.

Remaining Oil Distribution Law and Potential Tapping Strategy of Horizontal Well Pattern in Narrow Oil Rim Reservoir with Gas Cap and Edge Water

For thin oil rim reservoir with gas cap and edge water, it is helpful to improve the development effect to find out the distribution law of remaining oil in this kind of reservoirs. For this reason, taking the narrow oil rim reservoir with gas cap and edge water of Oilfield A in Bohai Sea as a case, the main controlling factors, including reservoir structure, fault, gas cap energy, edge water energy and well pattern, affecting the distribution of residual oil in this kind of reservoir were analyzed by using the data of core, logging, paleogeomorphology and production. Then, the distribution law of remaining oil was summarized. Generally, the remaining oil distribution is mainly potato-shaped or strip-shaped in plane. Vertically, it depends on the energy of gas cap and edge water. For the reservoir with big gas gap and weak edge water, the remaining oil mainly lies in the bottom of oil column. And for the reservoir with small gas gap and strong edge water, the remaining oil mainly locates at the top of oil column. Aiming at different distribution modes of remaining oil, the corresponding potential tapping strategies of horizontal wells are put forward: in the late stage of development, for the reservoir with big gas gap and weak edge water, the remaining oil concentrates at the bottom of the oil column, and the position of horizontal well should be placed at the lower 1/3 to the lower 1/5 of the oil column;for the reservoir with small gas cap and strong edge water, the remaining oil locates at the top of the oil column, and the position of horizontal well should be put at the upper 1/5 to the upper 1/3 of the oil column height, vertically. Based on the study on remaining oil of Oilfield A, a potential tapping strategy of well pattern thickening and vertical position optimization of horizontal well was proposed. This strategy guided the efficient implementation of the comprehensive adjustment plan of the oilfield. Moreover, 18 infill development wells were implemented in Oilfield A, and the average production of the infill wells is 2.1 times that of the surrounding old wells. It is estimated that the ultimate recovery factor of the oilfield will reach 33.9%, which is 2.3% higher than that before infilling wells. This study can be used for reference in the development of similar reservoirs.

Classification of carbonate gas condensate reservoirs using well test and production data analyses

Carbonate reservoir patterns play an important role in the production performance of oil and gas wells,and it is usually classified through static data analysis which cannot reflect the actual well performance.This paper takes the Tazhong No.1 gas field in the Tarim Basin,China as an example to investigate the classification of carbonate reservoirs.The classification method mainly combines well test analysis with production analysis—especially the Blasingame type curve method.Based on the characteristics of type curves for well test analysis and the Blasingame method,the relationship between the type curves and reservoir pattern was established.More than 20 wells were analyzed and the reservoirs were classified into 3 major patterns with 7 sub-classes.Furthermore,the classification results were validated by dynamic performance analysis of wells in the Tazhong No.1 gas field.On the basis of the classification results,well stimulation（i.e.water flooding in a single well） was carried out in three volatile-oil wells,and the oil recovery increased by up to 20%.

Analysis of Changing Landscape Pattern in Baiyangdian before and after Ecological Water Supplement Project Based on RS and GIS

By using TM remote sensing images of Baiyangdian Wetland in 1989,1999,2003 and 2004,taking the water area between Anxin County and Cangzhou where most of Baiyangdian Wetland water body lies for landscape classification,changes in landscape pattern of Baiyangdian before and after the water supplement were analyzed with landscape indexes calculated by Fragstats3.3. The results showed that after the water supplement,from the perspective of landscape cell index,fractal dimension of major ecosystems in Baiyangdian decreased to some extent;from the perspective of landscape diversity index,diversity index of the study region also decreased,which demonstrated that ecosystem diversity in this region reduced,land cover grew to simplification;and the decreasing evenness degree of the study region also showed the uneven development of its ecosystems. That is to say,water supplement has brought favorable ecological changes to the eco-environment of Baiyangdian,which has further optimized the health condition of ecosystems in this region.

海上大井距高强度蒸汽吞吐开发规律及开发策略

海上稠油资源丰富,热采开发需求大,经过多年实践,实现了对薄层稠油、边底水稠油和特—超稠油的蒸汽吞吐开发。准确认识海上稠油油藏大井距蒸汽吞吐的渗流特征和蒸汽吞吐开发规律,进而对热采开发效果和开发状况准确评价,成为海上稠油热采开发方案设计、调整、优化和增产增效的关键。通过对热液区实际温场分布和蒸汽超覆现象定量化表征的研究,表征加热半径变化,总结海上大井距蒸汽吞吐的产量递减、有效期、生产压差、伴生气的规律和开发经验,确定了海上蒸汽吞吐的3个递减阶段和平均递减率。在此基础上,通过使用油藏数值模拟方法进行预测,提出了海上稠油油藏大井距蒸汽吞吐的开发策略。海上大井距蒸汽吞吐型开发推荐水平井,边水油藏在距离内含油边界150~200 m以上布井,采用高干度、大周期注入量提高地层热利用率,海上大井距热采平均有效期为329 d,第一周期平均月递减率为13.5%,生产井的合理生产压差介于3.5~5.0 MPa。研究结果对海洋石油稠油热采规模化开发具有一定的指导意义。

低渗透油藏压驱裂缝展布特征及影响因素

压驱技术为低渗透油藏效益开发探索出了新途径,但尚有诸多机理问题认识不清。针对压驱注水涉及岩石断裂损伤过程,基于三轴应力流固耦合实验装置、智能渗透率场反演装置和微米CT扫描装置等,建立了压驱物理模拟方法,明确了压驱裂缝展布特征及影响因素。结果表明:压驱注水对井周岩石造成区域性非均衡损伤,储层岩石在较大排量范围内均有破裂特征;压驱裂缝展布受注入流体黏度、排量影响,在注入参数达到岩石破裂条件下,注入排量和流体黏度越低,越有利于形成复杂缝网,随着注入流体黏度和排量的提高,压驱裂缝开度增加。研究成果可为现场压驱提供理论指导。

A Study of the Genesis of Karst-type Subtle Reservoir in Tahe Oilfield

The genesis of the Ordovician karst in the Tahe Oilfield is hypothesized on the basis of many analyses of the geo-chemical data and the sporopollen. Ordovician carbonate rocks experienced multistage karst reconstructions under the condition of low-temperature oxidation meteoric water on the surface or near-surface. The karst occurred mainly in the early Hercynian, which has undergone three stages of karst cycle and developed three sets of cave reservoirs under the influence of the tectonic uplift, and the upper of the cave was formed earlier. The evidence of karst was found in the Caledonian. On the above basis, the genetic prediction pattern of the Ordovician palaeokarst reservoir in this region was set up.

Performance analysis and optimal design for well patterns in anisotropic formations

The mechanism of the effects of anisotropic permeability on well patterns and reservoir development are investigated by coordinate transformation, fluid flow analysis, and reservoir development concepts. Anisotropy of permeability has reconstructive effects on well patterns. The originally designed flooding units are broken up, and new pattern units are made up of the wells that belong to different original units. The behavior possesses strong randomness, and leads to a complicated relationship among the injection and production wells, and unpredictable productivity of the formations. To prevent the break-up of well patterns, well lines should be either parallel or perpendicular to the maximum principal direction of the anisotropic permeability （i.e. the fracture direction）. To optimize the development effects ofanisotropic formations, the latitudinal and longitudinal well spacing of the well network are calculated from the principal values of the anisotropic permeability.

Plankton community composition in the Three Gorges Reservoir Region revealed by PCR-DGGE and its relationships with environmental factors

To explore the relationships between community composition and the environment in a reservoir ecosystem, plankton communities from the Three Gorges Reservoir Region were studied by PCR-denaturing gradient gel electrophoresis fingerprinting. Bacterial and eukaryotic operational taxonomic units （OTUs）, generated by DGGE analysis of the PCR-amplified 16S and 18S rRNA genes, were used as surrogates for the dominant ＂biodiversity units＂. OTU composition among the sites was heterogeneous; 46.7% of the total bacterial OTUs （45） and 64.1% of the eukaryotic OTUs （39） were identified in less than half of the sampling sites. Unweighted pair group method with arithmetic averages （UPGMA） clustering of the OTUs suggested that the plankton communities in the Xiangxi Rive sites were not always significantly different from those from the Yangtze River sites, despite clear differences in their environmental characterizations. Canonical correspondence analysis （CCA） was applied to further investigate the relationships between OTU composition and the environmental factors. The first two CCA ordination axes suggested that the bacterial community composition was primarily correlated with the variables of NO3^--N, dissolved oxygen （DO）, and SiO3^2--Si, whereas, the eukaryotic community was mainly correlated with the concentrations of DO, PO4^3--P, and SiO3^2--Si.

中上扬子地区震旦纪灯影组沉积期碳酸盐岩台地古地理格局及有利储集相带分布规律

【目的】中上扬子地区灯影组沉积期碳酸盐岩台地古地理格局及有利储集相带发育分布规律尚存争议,阻碍了灯影组油气勘探领域由绵阳—长宁拉张槽两侧向其他广大地区拓展。【方法】通过中上扬子地区灯影组30余条剖面(钻井)开展岩石类型划分及沉积相分析,【结果】进一步明确丘滩相以块状砂屑/鲕粒白云岩及柱状、穹窿状叠层石白云岩为特征,呈环带状分布在中上扬子台地(或内缓坡)边缘,向外过渡为中—外缓坡风暴岩或斜坡—盆地相区的滑塌角砾白云岩、泥质白云岩、硅质岩等。由于丘滩的阻挡作用,其内侧以低能的潮坪及潟湖沉积环境为主:其中潮坪相主要发育微生物纹层白云岩、穹窿—缓波状叠层石白云岩、凝块石白云岩夹砂屑白云岩、泥晶白云岩,纵向上常常形成米级—厘米级旋回;潟湖相主要由泥晶白云岩、含球粒/砂屑泥晶白云岩组成。相带时空分布表明灯影组在中上扬子地区总体呈现出进积的沉积趋势,内部包含2.5个层序,即三次进积(变浅)和两次退积(变深)旋回。【结论】由于灯影组在台地边缘—斜坡区域普遍遭到剥蚀,以及灯影组沉积期上扬子台地范围远超目前的板块边界,灯影组上部灯四段很少发现高能丘滩相带。在此背景下,局部地区(如松林—岩孔地区、中扬子台地周缘)灯影组中下部灯一段—灯二段(或蛤蟆井段、石板滩段)发育的丘滩相,是重要的有利储集相带。此外,处于海退体系域的灯二段中下部和灯四段上部(或相当层位)在中上扬子台地(或内缓坡)内部广泛发育微生物白云岩,也为储层发育有利相带。在中上扬子台地微生物白云岩广泛分布的背景下,进一步分析优质储层发育机理与分布规律才是找到油气接替区的关键。

Experiments on nitrogen assisted gravity drainage in fractured-vuggy reservoirs

Visual models of fractured-vuggy reservoirs were designed and manufactured to conduct experiments of nitrogen assisted gravity drainage(NAGD). The impacts of flooding pattern, gas injection rate, well type, and displacement direction(vertical or horizontal) on development performances and remaining oil distribution were studied. The results show that during NAGD, the sweep scope is decided by the connections between producer and reservoir, and the local sweep efficiency is decided by fracture-vuggy configuration. The homogenous fractured reservoir has higher oil recovery, and the bigger the aperture of fracture is, the higher the recovery. The main regions of remaining oil due to poor connectivity and gas-oil gravity difference include blind fractures and vugs below the connected fractures, the bottom of vugs, and the narrow and low-angle fractures. The accumulation of remaining oil in the bottom of reservoir is easily formed and controlled by the connections between producers and reservoir. The higher the gas injection rate and the stronger the fracture heterogeneity, the earlier the gas channeling and the lower the oil recovery of the producer will be.Horizontal wells have the best development effect, so horizontal well can be applied in fractured-vuggy reservoirs without bottom water.Producers should be preferentially drilled at low structural position. Gas channeling firstly occurs in the producer at high structural position, and it should be shut in timely to improve the utilization of injected gas.

四川盆地东部上石炭统黄龙组规模储层形成主控因素与发育模式

石炭系黄龙组是四川盆地东部地区(以下简称川东地区)重要的天然气产层之一,石炭系储层是控制气藏发育的关键因素。为了深入评价川东地区黄龙组储层,拓展勘探新领域,寻找接替区,在前人研究的基础上,应用大量钻井、岩心、露头和分析化验等资料,系统研究了黄龙组储层发育的主控因素和发育模式,并预测规模储层的展布。研究结果表明:(1)黄龙组储集岩主要为颗粒白云岩、角砾白云岩和晶粒白云岩,储集空间主要为晶间孔/晶间溶孔、粒间溶孔/粒内溶孔、溶洞和裂缝,颗粒滩为有利储集体,裂缝-溶蚀孔洞型储层质量好;(2)储层发育主要受乐山—龙女寺古隆起和开江古隆起、沉积作用及成岩作用的共同控制,古隆起控制颗粒滩分布和准同生期成岩作用,是规模成储的基础,准同生期白云石化作用、层间岩溶和风化壳岩溶作用的叠加是形成规模储层的关键,喜马拉雅构造运动产生大量构造裂缝,提高了储层的渗滤性和规模性;(3)一定厚度和较大面积的Ⅰ—Ⅲ类储层可形成规模储层区,对5个规模储层发育区进行了评价,已发现气藏主要分布在这5个区域的背斜构造部位。结论认为,川东地区石炭系仍有较大的天然气勘探开发潜力,向斜区发育大面积的规模储层,是下一步天然气增储上产的重要方向。

Study on Rational Well Spacing Optimization of Low Permeability Gas Reservoir

The Shanggu gas field is the low porosity and low permeability. Single well controlled reserves, economic limit well spacing and economic rational spacing through different methods are calculated. With the development experience of Su Lige gas field as guidance, the rational spacing of Shanggu gas reservoir is 700m×900m by calculating daily gas production rate and cumulative gas production with different well spacing using numerical simulation method.