运移优势通道方向的研究方法及应用(英文).doc

Types and research methods of the dominant migration pathwaysJIANG Fu-jie1,2, PANG Xiong-qi1,2, JIANG Zhen-xue1,2,MA Xing-zhi1,2, ZHOU Xiaohui1,2 (1.Basin and Reservoir Research Center of China University of Petroleum, Changping District 102249, Beijing; 2.Key Laboratory for Hydrocarbon Accumulation Mechanism of Education Ministry, Changping District 102249, Beijing; 3. Strategic Research Center of Oil and Gas Resources, Ministry of Land and Resources 100034, Beijing)Abstract: the research on the dominant migration pathways is the basis of tracing migration direction accurately and predicting exploration destination. The dominant migration pathways do exist and has been verified by geologic analysis and numerical simulation, but its research methods are not perfect. This paper points that there are four basic patterns of dominant migration pathways: dominant migration pathway with different levels, with separation trough, with fluid pressure, and with preponderant flow direction. Based on analysis of affecting factors about the four basic patterns, and comprehensively considering the underside cstructural features of cap rocks , hydrodynamic condition, accumulation sand bodies, fault characters, this paper develops two research methods: single-element superposition analysis and multi-element superposition analysis. Using these two methods, this paper predicts the dominant migration pathways of middle accumulating grouping with a credible consequence at Binbei areas in Songliao Basin. There are two directing dominant migration pathways in the middle accumulating grouping at Binbei areas, which links different source rocks separately. Multidisciplinary analysis indicates that its feasible to predict the dominant migration pathways by using the two methods.Key words: migration of oil and gas; dominant migration pathways; Binbei areas in Songliao BasinThe research on the secondary migration pathways is the basis of tracing migration direction and locating reservoir position, it can guide exploration of hydrocarbon efficiently. As the migration pathways are affected by many factors, the research of it remains a focus of petroleum geology. It is indicated that the secondary migration of hydrocarbon only passes through limited dominant pathways and the space of migration is merely 1%10% of the entire transport layers1-7,while the hydrocarbon migrated through which is a large part. As a result, the research on the dominant migration pathways is more and more appreciated by petroleum geologists.1 The overview of the dominant migration pathwaysThe dominant migration pathways are hydrocarbons main pathways in the secondary migration without extraneous interference and the result of the following elements, such as transport systems anisotropism, energy non-homogeneity ,fluid flowing and so on6,8,9. It can be fault, unconformity or transport layers with high porosity and permeability. The dominant migration pathways are the pathway of the prior choice of hydrocarbon, but not the tendency. The dominant migration pathways is only a small part of transport system, but it can transport large part of hydrocarbon. Geologic analysis and experiment research of physical analogy show, hydrocarbon always moves along the direction of the minimum friction and the maximum component1,14-15. There are four basic patterns of dominant migration pathways6,16: (1)dominant migration pathway with different levels, (2)dominant migration pathway with separation trough, (3)dominant migration pathway with fluid pressure, (4)dominant migration pathway with preponderant flow direction Among them, dominant migration pathway with fluid pressure is different from dominant migration pathway with preponderant flow direction. The former is controlled by fault dip and buoyancy, and the latter is controlled by dynaflow and buoyancy.Although there are four basic patterns of dominant migration pathways, it is difficult to discuss the predictive methods further due to the influence of the complicate geologic situation and datas accuracy. This paper provides two valid methods to predict the dominant migration pathways, which has been proved effective subsequently.2 The basic types of the dominant migration pathways2.1 dominant migration pathway with different levelsThe dominant migration pathway with different levels is formed in the transport layers due to different structure of porosity and permeability6,16. Fig.1() shows the model. Hydrocarbon always migrates forward by way of the dominant migration pathway with maximum different levels. The different level means the difference between the porosity and permeability of pathways and the peripheral medium. The bigger the difference is, the easier hydrocarbon migrates. 2.2 dominant migration pathway with separation troughThe separation trough means the position of the separation trough of regional seal above the transport layers is different from the one of active source, which controls the fractional flow of hydrocarbon. The separation trough of regional seal deviates from the center of source rock and moves to the opposite direction6,16. The model is showed in Fig.1(). In this model, the buoyancy is the main force during the hydrocarbon migrates upwards. The separation trough which formed in the bottom of seal can decide where the hydrocarbon migrates to. 2.3 dominant migration pathway with fluid pressureThe fluid pressure can control the direction and quantity of migration in the process of hydrocarbon migration6,16. The model is showed in Fig.1 (). Without stream force in the uniform transport layers, the hydrocarbon can migrate from deep to shallow in the basin by buoyancy. Conversely, the direction and pathways of migration can be influenced by buoyancy and stream force. The hanging reservoir formed when the direction of buoyancy and stream force is contrary but with the same strength. When the direction is the same, the hydrocarbon will migrate forward fast. 2.4 dominant migration pathway with preponderant flow direction.The preponderant flow direction means that the fault dip and buoyancy can control the direction during migration 6,16. The model is showed in the Fig.1 (). In the sedimentary basin, the porous medium are filled with groundwater, and hydrocarbon is always affected by buoyancy, so the hydrocarbon migrates from the center of basin to the edge, from deep to shallow. When the fault appears, hydrocarbon migration is influenced necessarily by buoyancy and fault section (reservoir). The bigger the dip is, the easier the hydrocarbon migrates upwards. Fig.1 model of the dominant migration pathways3 The research methods on the dominant migration pathwaysAs for a sedimentary basin, hydrocarbon goes into the reservoir during the first migration and then accumulates in the proper trap finally, and it is a complex geological process which is influenced by many factors so that it is very difficult to predict the dominant migration pathways. The practical exploration indicates that about 70% of the hydrocarbon-bearing pool locate in the dominant migration direction in sedimentary basins16. Therefore, as long as the direction of hydrocarbon dominant migration pathways are predicted , could the exploration be effectively guided. And it is easier to operate since the method evades many constraint factors during the prediction of the dominant pathways. In this case, we put forward two ways of prediction. The first one: the complex geological course can be devided into simple geological factors, which can be analyzed comprehensively and superpositioned in the plane ;The second one: for some place, the weights of different influence degree of the factor are not the same. Hence, carrying on the weight of various kinds of influence factors and giving them scores, and then superposing them is an valid way to determine the migration direction. The research will make the result of predicting more accurate. Based on this, the paper develops two research methods. 3.1 The method of single-element superposition analysisThe basic thought of this method is to analyze the basic mode of the four kinds of the dominant migration pathway one by one, and then map them on the plane, superpose the dominant migration pathways of four types in the same system of coordinates. The area where the four factors overlap most is a distribution range of the dominant migration pathways (Fig.2). This method has been used in the Qaidam Basin and achieved a big success17. The following is a brief overview of the research method of every single element.3.1.1 determination of the dominant migration pathway with different levelsAccording to the reasons that cause different levels of reservoir, the dominant migration pathways could be discriminated by the growth and physicality characteristics of the reservoir sand. The area with the better presence of sand, the higher porosity and permeability is more favor for hydrocarbon migration. In the practical apply, due to the rare core stone analysis data of physicality parameters, the fitting calculation of physicality parameters is adopted using the well log interpretation, for example ,using the acoustic to fit porosity and permeability. This method is widely used and the fitting value is credible to make up the insufficiency of the real data.3.1.2 determination of the dominant migration pathway with separation troughSegregation advantage is produced by the divergence of the structural styles of caprock in hydrocarbon accumulation play that result in the inhomogeneity of the hydrocarbon migration amout in different migration direction. The structural maps of the underside caprock can be utilized to analyze the migration direction with separation trough. For a certain research area, the mature seismic exploit provides a favorable data for the working out of structural maps. So the dominant pathways with separation trough could be determined by the segregation direction of the caprock underside.3.1.3 determination of the dominant migration pathway with fluid pressureUsing the stratum pressure data to obtain the hydrodynamic stress contour of the research area, then according to the decease change of the contour from high to low to ascertain the direction of the dominant migration pathway. The data used are primarily stratum testing data, and could be combined with logging data to fit the pressure and make up .3.1.4 determination of the dominant migration pathway with preponderant flow directionIt is complex to ascertain the dominant migration pathway with preponderant flow direction, because it includes considering the fault inclination and dip and analyzing the time of fault opening especially during the process of migration. The study should have the aid of geological and geochemical method.3.2 The method of multi-element superposition analysisThe basic guiding ideology of this method is processing various kinds of geological elements that affect the hydrocarbon dominant migration direction, combing geological analysis to attain the weights of the diverse elements, then superposition the data to draw charts in plane. Finally, according to the contour variation trend to discern the direction of dominant migration pathways(Fig3). 3.2.1 data normalization To different district, there is a difference of the action strength among the four basic modes of the hydrocarbon dominant migration pathway on account of diverse geological condition. So in order to reflect the impact of different mode and eliminate the deviation caused by different magnitudes, we processed the basic geological data with dimensionless, usually adopt the graduation normalization to transform the data into the range of 0 to 1(show as equation 1). (1)3.2.2 data griddingAfter the normalization, using grid the basic geologic materials (including the bottom surface structural configuration of seal, the characteristic distributed of the sand body, the stream force situation, the fault characteristic, etc.) which can reflect the different kinds types of the dominant migration pathways pathways,to grid in order to form the the same data file with the same grid, and then give the value factors weight according to the their function degree finally. 3.2.3 data superposition There are three kinds of data processing methods for basic geologic data file (equation 2-equation 4). After data processing, we can obtain combined geologic information, and then can obtain the distribution characteristic of the dominant migration pathways. The superposition of product: By multiplying the data of kinds of basic geological information at the same points in the platform, the combined geologic information can be obtained. It is suitable for the product of the geologic information data represent a new geologic variable, or have a certain specific geological meaning. (2)The accumulative superposition: By accumulating the data, the combined information can be obtained. It is suitable for the data whose relation between various kinds of geological information after superposition is not clear; the result of accumulation represents the sum of the geologic information. (3)The minimum superposition: Using the minimum of the data of kinds of basic geological information of the same points in the platform as superposition, the combined information can be obtained. The weakest factor principle: (4)Here, Ty is the prediction data of the dominant migration pathways, and F1、F2、F3、F4 are the data of the superposition of the geologic information data. A、B、C、D are the weight of the geological factors. Fig.2 flow chart on predicting the dominant migration pathways by using single-element superposition analysisFig.3 flow chart on predicting the dominant migration pathways by using multi-element superposition analysis4 Example4.1 The geological overviewBinbei area is located in Songliao Basin and refers to the areas to the north of the railway line of Binzhou, to the west of Nenjiang, nearly 8104km2 of area. The middle and shallow structure was mainly divided into four primary structural units and twelve secondary structural units. The primary structural including: the north of the western slop area, the entire northern disappeared area, the north of the middle depression area, and the large part of the northeastern uplift area (Fig.4). The Binbei area mainly developed Cretaceous formation which was overlaid by Tertiary Formation Quaternary Formation. According to the source-reservoir-seal assemblage, the middle and shallow layers were divided into two parts: the shallow accumulating group and the middle accumulating grouping. Here, the accumulating group means the source-reservoir-seal assemblage under the similar conditions. The main work of this paper focuses on the middle accumulating group. The source and seal of the middle accumulating group are from K1qn1, the reservoir is K1q3+4 (Fuyang). Since 1960s, 101 wells have been drilled in this area; among them, one well has commercial gas flow, two wells with low, and fifteen wells with SG&O.Fig.4 middle and shallow structure zoning chart at Binbei areas（modified from Daqing research institute, PetroChina 1990）4.2 The method of single-element superposition analysis4.2.1Direction of dominant migration pathway determined by separation trough The seal of the middle accumulating group is K1qn1. The seal has been steadily since the critical time of hydrocarbon migration and accumulation in the late Cretaceous. Two ridge-like structures, which respectively exist in the Keshanyilong anticline and near the Dong 5 well, is the priority selection directions of hydrocarbon migration pathways. And both the two ridges display into NNE incline anticline which could control the migration direction on a large scale.4.2.2 Direction of dominant migration pathway determined by different levelsTwo regions with high value of porosity and permeability exist in the Fuyang reservoir sandstone.One region extends from the Sanzhao depression to the northeast direction along the Suihua depression, which connects with the source rock in the Sanzhao depression, and the other extends towards Keshanyilong anticline and Sanxing anticline from Wuyuer depression,which connect with the source rock in the Heiyupao depression and the Wuyuer depression respectively. As both the two belts have high porosity and permeability and the distribution area is relatively wide, it is difficult to ascertain the lower limit of physicality. Consequently the direction of the dominant migration pathway is represented by two high porosity and permeability belts, and the arrowhead in the belts indicate the optimum migration pathways (Fig.4).4.2.3 Direction of dominant migration pathway determined by fluid pressureThe test of the reservoir water head indicated that there were two direction of the pressure release. The first one is the high value zone from Sanzhao depression towards northeast along Suihua depression,that is,where the Dong 5 well locates. The second one is belt from the Heiyupao depression and Wuyuer depression to Keshanyilong anticline along the NE direction.The fluid pressure superiority exhibit as a ribbon. Because the fluid pressure decrease precipitously and the scope is wide, it is hard to ascertain the lower limit. The arrowhead shower the optimal migration pathway (Fig.4).4.2.4 Direction of dominant migration pathway determined by preponderant flow directionThe fault strike in the Fuyang reservoir is primary NNW, and the fault scale is small. The layers cut off by the faults is rare and all the seal has not been cut through. Therefore, the transport function of the faults mainly concentrated on the lateral direction.It is a favorable direction along the fault strik