The Relationship Between Reservoir Characteristics And Gas-water Distribution Pattern In S₂³ In Z3-Y80 Wellblock, Zi-Zhou Area

Zi-Zhou gas field is a main gas-production zone in the Ordos Basin and the S2 gas field has a proven gas reserve of 922.6×108m3 by 2005. With the exploratory development, as the gas production developed in large area, a great many water production wells appeared in this field. There were totally 31 water production wells and their production varied from 0.3m3/d to 46.6m3/d. These wells had badly influenced the development effects and development process of this area, especially increased the risk of the disposition of exploitation wells. So we should find the gas-water distribution pattern and forecast the gas-water distribution in the researching area as to enhance the deployment success ratio and to build up higher deliverability. So it is very important to study the reservoir characteristics and gas-water distribution pattern of this area immediately.The paper researches the distribution of the sand-body and the characteristics of reservoir in Shan-2 member. Member comparisons and connectivity is studied based on the high resolution sequence stratigraphy methods; the fluid recognition in single well is studied by the methods of cross plot and normal distribution using well log data; we have also studied the gas-water distribution in profile; with data of hydrochemical water information, we have acknowledged the pattern and controlling factors of gas-water distribution and we have pointed out the favorable exploration targets. The results are:1. The basal sand body of S23 is steady, middle–head of the sand body is understable and the sand body along the river channel is well connected. The S23 reservoir belongs to low porosity and permeability reservoir; its pore types are mainly intergranular pore and intergranular dissolved pores and the pore structure is good. The reservoir are mainly composed of typeⅡ,typeⅢ. The reservoir conduct intensely leterogeneity in plane and internal. 2. The S23 is divided into a middle base-level cycle which contains three short-term base-level cycles. All of the short-term base-level cycles, the SSC2 and SSC3 cycles are widespread in the area and the SSC1 cycle is lost in several wells. The lithology of the SSC1 cycle is mainly black marine mudstone or marine limestone of the top of Taiyuan formation, these stones were used to fill and level up during the period of continental oceanic facies varied. The 3rd member of Shan-2 formation contained two types of sequence structures which are asymmetrical cycle sequences (Type A) and symmetrical cycles sequences (Type C). The sequence structures are divided into 4 sub-types. From the study of the high resolution stratigraphy frameworks we know that there are two sand bodies in the S23. The sand bodies grow in the SSC2 and SSC3 short-term cycles separately. The SSC3 short-term cycle is under-developed in the north of the research area. The sand bodies superposes from Zhou 35-28 to Yu64 well fields in the middle of the research area.3. S23 water is CaCl2 and belongs to residual water in the formation. We have identified two types of formation water: edge and bottom water (salinity>100g/L) and lenticular water (salinity<80g/L). The wells that produce edge and bottom water are mainly in the downstructure location and yield much water and little gas; the wells that produce lenticular water are in the relatively higher location or at the edge of the main sand-body and they yield a little water with some incidental gas.4. Affected by the structural feature and the distribution of sedimentary facies, the sand body of S23 in the research area ranges from north to south in a banded shape, the northern part of the sand body is thicker while the southern part is thinner; two gas-rich zones are located in the southern and northern part of the main sand body; in each of the gas-rich zones, edge water zones exist in the south and southwest downstructure location, which forms two gas-water interfaces in the research area; the east part of the main sand body is affected by the reservoir characteristics, it is tight sand with high water-cut and usually produces little or no fluid when testing, it is mainly dry bed.5. Research results demonstrate that the sand body near Y48 is thicker,with good reservoir properties and far away gas-water surface , and it is the advantageous exploration area.