Research On Reservoir Development Adjustment Program For Xishanyao Formation Of Cai9Wellblock

With the continuous development of domestic oil field development, conventional high permeability reservoirs have gradually got into mid-high water cut period. With oil production level decreased quickly and stable foundation was weak, it is more and more difficult to take development adjustment. Also this situation can’t meet China’s national economic and social development of energy urgent needs. In this case, low permeability reservoirs which are considered of no use began to enter the research field of petroleum technology workers. China is rich in natural resources and vast in land, also low permeability oil and gas resources are very rich. It is of great value to do some research on it. In this paper, our target reservoir named Xishanyao Formation of Cai9well block is also such reservoirs.Compared with conventional mid-high permeability reservoirs, low permeability reservoirs have some particular feature, such as large proportion of pore volume that connect with small pore throat, large surface to volume ratio, large rock oil coat, evident capillary tube effect, evident Jamin action, serious jam and break appearance and small moving fluid saturation. Based on the seven reasons, the seepage flow in low permeability reservoir is characterized of non-Darcy flow, two-phase flow, fluid and solid coupling and imbibition. Due to the presence of these seepage flow environment and characteristics, low-permeability reservoirs development process also have some different characteristics, such as natural energy shortage, low water drive susceptibility, output of production wells decreased quickly after water breakthrough, serious fractured water channeling and low water cut period to be the main oil production period.In order to improve the development effect of low permeability reservoirs with great potential, geological worker at home and abroad who are studied on oilfield development conducted a large number of indoor field research, which has achieved abundant practical results. At present, foreign technology in the low permeability reservoirs is as below:the rational deployment of injection-production pattern, diminishing the well spacing, the gas injection development, the high density perforating technology and the horizontal well technology. At home, the technology in the low permeability reservoirs is as below:formation fracture description and optimization of injection-production pattern, the reservoir protection technology range from drilling, completion and water injection to other operations, the efficient perforating technology, the fracturing technology, the development plan diminishing the well spacing and infilling well pattern, the injection of synchronous in the early water injection, the horizontal well technology and so on. Based on a series of development technology, in view of the low permeability reservoirs, domestic and foreign have researched a series of enhanced oil recovery on the low permeability oil. Which include the polymer flooding technology, the gas injection production technology and so on.In1992April, the Xishanyao Formation of Cai9well block reservoir tested in Xishanyao Formation of Cai002well block, we obtained industrial oil flow and found it was a low amplitude anticline reservoir cutting by faults and becoming complex. The proven reserves are2162.75×104t, with characteristics like low porosity, low permeability and the local microcrack development. Since1993it is developed in300m inverted nine spot well pattern. Until2012August, the reservoir has307wells, including235oil wells,60developed wells which account for25.5%of the total number. Nissan liquid level is722t, nissan oil level is76t, composite water cut is89.4%, liquid production rate is1.22%, oil recovery rate is0.13%, cumulative liquid is951.7×104t, cumulative oil is489.6×104t, the degree of recovery is22.64%.Xishanyao Formation of Cai9well block is an ultra low permeability reservoir with complicated geological conditions. Part of the regions is natural microcrack developed with the serious phenomenon of water sensitivity. In the early phase of the development process, because of the unclear understanding of the reservoir geological characteristics, we took the large well spacing development, intensive injection and production and ignored the water flooding policy, leading to a low current rate of oil production and poor development effect. Specific performance:(1)many shutting wells, low utilization rate of oil well, reduced producing degree of reserves;(2)The reservoir water flooding effect is poor, the recovery rate is far lower than the calibration level prediction;(3)The reservoir damage is severe, the flow capacity is substantially reduced;(4)The existing well pattern adaptability is poor.To get better reservoir development effectiveness and improve the ultimate recovery and development economic benefit of Xishanyao Formation of Cai9well block, this study conducted in the early dynamic analysis on the basis of the reservoir, and the development status of the development of the course are described. All of these work is trying to find the cause of the current development status with poor control factor. A series of geological processes and adjustment measures taken in the early development process were analyzed and evaluated by analyzing changes in production wells before and after adjustment, pointing out the pros and cons of these adjustment policies for post-adjustment guidance to determine policy.At the same time, the paper also uses empirical formula method, water drive curve method, Tong’s chart method, decline curve method for the prediction of reservoir recovery. The average recovery prediction value of the block from various methods is26.25%and the recoverable reserve is5677200tons. We obtain the efficiency of displacement of oil by water (43.1%) by oil phase permeability curve. This is the largest recovery that Xishanyao Formation of Cai9well block can get. And it’s also the potential of Cainan Oilfield development adjustment.According to the previous analysis of statistical results and geological experts’ advice from owner, we base on the effective thickness of bigger single well cumulative oil recovery affecting factors and the initial oil saturation weighted, and with reference of the tectonic location, injection production well pattern type, sedimentary microfacies distribution and then divide the reservoir. The analysis indicates that the south central part of reservoir is located in high position, the reservoir thickness is large, sedimentary microfacies are underwater distributary channel, sand body distribution is relatively uniform, crack growth is little. It’s a yield region and has many currently open wells, of which production capacity is currently the main contribution to the region. The central area and the row-column area have potential. Due to the higher injection production ratio of the central area, there is no prominent development effect by conventional water flooding. Thus, gas drive and intermittent water flooding can be considered in later adjustment. The row-column area has been injected and exploited intensively in early times, which causes widespread flooding water channeling, large amount of shut-in wells. The next step is to focus on the profile control of water injection well and water shutoff. The edge area is located in the edge of the reservoir, effective thickness is thin, the remaining reserves are little. Thus, the main consideration can be reservoir simulation.Based on the pre-dynamic analysis and research of reservoir assessment, a test area has been chose to illustrate the appropriation of infilling well pattern, and return adjustment by numerical simulation. On the basis of original geometric model, as the simulation result shown, with the combination of plan3and4will got the optimum developing effect, firstly, infilling injection wells between the original reverse nine-spot well pattern and corner well, make it a inregular well pattern, forming a diamond five-spot well pattern. Later, returning the production well of sangonghe formation to Xishanyao, forming a Combined well pattern with triangle well pattern, five-spot pattern and diamond five-spot pattern.Micro fracture has developed at reservoir central area and most of the fractures are high angle fracture. Most of oil wells of this area were shut-in because of the high water cut and water flooding development adjustment has no significant potential. According to the air drive reservoir suitable conditions, this area is fit for air injection flooding. First we can do some oil field experiment and spread it to the whole area according to the test results. In addition, well pattern deployment one-off simulation studies also have been done in this study for low permeability reservoir. And the results show that, it is better to take small well spacing pattern in the early development period than in the late period. It will finally achieve better development effectiveness and the ultimate recovery of the reservoir is higher.