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The Study of Favorable Reservoir Facies from Low Permeability Reservoir of Chang 8 Member of Yanchang Formation in Zhenjing Block, Ordos Basin, China

Author: WangYuZhu
Tutor: ZhaoYanChao
School: China University of Geosciences
Course: Energy Geological Engineering
Keywords: Zhenjing region favorable reservoir facies mud invasion model high production genesis favorable area predicted
CLC: P618.13
Type: Master's thesis
Year: 2010
Downloads: 123
Quote: 1
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Abstract


The Chang 8 Member is not only an important formation we study now, but also the mian production zone to achieve the aim of output of one million tons of crude oil per year in Mesozoic of Zhenjing Block, Ordos Basin. Since 2008 Zhenjing 5 well area has been put into development, high production oil and gas has been obtained in the Chang 8 Member in various locations. Thereby, it directly promotes that the HH16~HH105 well area exploration and development integrated experimental area was established, and takes exploration and development in Chang 8 Member a new look. Nevertheless, although a major breakthrough has been achieved in Chang 8 Member, there is a large distance from the target of output of one million tons per year, especially, the key controlling factors on high production of lower permeability reservoir are not clear, and it is difficult to determine distribution of favorable reservoir facies.Firstly, the sedimentary features of Chang 8 Member have been studied on the basis of core, petrographic thin section and grain size data. The framework of stratum has been established by the guide of systematically genetic stratigraphic analysis. And then, the distribution features of sandstone and depositional model have been studied by the use of logging data. It would be found that it is a set of braided river delta with distribution channel developed, which is the key sandstone reservoir and its trend and size determined the shape and scale of it in Chang 8 Member. It located in the both sides and the bottom of distribution channel for the mouse bar of smaller scale. The delta extended to the basin with a branch shape like tree.It has features of fine grain size, lower compositional maturity, lower porosity (about 9.5%) and permeability (about 0.233×10-3μm2), and complex pore structure (middle-fine pore throat type, and bad pore throat sorting) for sandstone reservoir of Chang 8 Member in target block. Nevertheless, since fracture was developed in reservoir of Chang 8 Member, it has been improved in the production capability of reservoir to a large extent.After lower threshold of reservoir of Chang 8 Member has been studied by Comprehensive use of capillary pressure curve and other data, it is considers that porosity is about 6%, and permeability is about 0.233×10-3μm2. Therefore, the reservoir can be divided into the fore types on the basis of porosity, permeability and parameters of pore throat.This paper makes a integrating evaluation for production zoon of Chang 8 Member, and divided into the five production types on the basis of oil output data, and in combination of indictor of oil output rate. Overall, it has features of lower permeability, lower structure relief and lower reserves abundance. All the wells product both water and oil without pure oil layer or water layer.This paper develops a method to identify fracture by use of correlation coefficient calculated between porosity and permeability on the basis core data. Three types reservoir has been divided for pore, pore-fracture and fracture types by correlation coefficient. The pore type reservoir can be reflected by porosity and permeability of matrix of rock because it is not effected by fracture, and the samples from the pore type reservoir can be used to build oil saturation model. The samples from the pore-fracture and fracture type reservoir can be used to build permeability logging interpretation model.Through analysis of the machenism of mud invasion, this paper has introduced an new index—saturation difference of mud (ASmf), which is the difference between the mud saturation of intermedient invasion zone and the invasion deeper zone. The result shows that the reservoir has great reservoir parameters and developed fractures whenΔSmf∈[0,1], it indicates that there is no fractures developed. WhenASmf<0, it indicates that fractures are developed,porosity and permeability of matrix of rock are better. WhenASmf>1, it indicates that fractures are developed, porosity and permeability of matrix of rock are poor. The permeability model has been established by the use resistivity logging data on the basis of above understanding. A indicator systems identifying tight degree of reservoir have been established byΔSmf. If ASmf> 0.6 has been considered as indicator of tight reservoir, it will give a proof to identify cement degree by logging.This paper determined the method of distinguishing oil and water reservoir. Three curves of Rd, Rs and Rxo respectively should be moved to the same position at the thick mud interval, and then, the relatiive position of these curves in sandstone interval indicates the production feature of reservoir. For instance, RXO<Rd<Rm represents high production oil reservoir. In addition, production function has been established by the guide of mud invasion model.This paper researched the differences between the good and bad reservoir, as well as the main controlling factors of the formation of favorable reservoir in Chang 8 section, Zhenjing region, through some aspects, such as sediment, structure, diagenesis and reservoir, on the base of formation testing data. The research found that sedimentation, structure, fracture, diagenesis, reservoir, heterogeneity, oil-abundance and relative permeability have obvious influence to the formation of favorable reservoir facies. Sedimentation determined the distribution of sandstone and the original reservoir parameters, at the same time, it influents the location where diagenesis occurred as well as its scale. Structure controlled the oil-abundance of reservoir. Fracture is one of the most important factors which influent the formation of favorable reservoir facies, attribute to its contribution in improving the reservoir parameters. On one hand, sedimentation reduced the reservoir parameters, on the other hand, it played a significant role in the formation of diagenesis trap, because it is resistant to the migration of oil and gas.In order to predict the location of favorable reservoir facies, this paper studied the distribution of the main controlling factors. The result showed that the folts present en echelon in the target region. Fractures always occurred in two locations, one is the place where occurred dense formation, the other is the area where the structural deformed greatly. calcite cementing belts always occurred at the place where the channel change direction.This paper considers that there are three kinds of trap in Zhenjing block, they are structural trap, lithological trap and diagenesis trap. Main type of structural trap is anticline fold, while lithology-structure strap occurred in the place where channel turned to the up dip direction of the monocline.On the basis of former research, this paper indicated the distribution of favorable reservoir facies, and defined five potential targets.

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