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The Pore Throats Structure And The Seepage Characteristics Of Gas And Water In Sulige Tight Sandstone Reservoirs

Posted on:2017-02-22Degree:MasterType:Thesis
Country:ChinaCandidate:Y H PengFull Text:PDF
GTID:2180330488950583Subject:Mineralogy, petrology, ore deposits
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Sulige gas field is the largest tight sandstone gas field in China, and it is also a typical "low permeability, low pressure and low abundance" gas reservoir, with strong heterogeneity, complex micro-nano-holethroats structure, strong sensitivity and non Darcy seepage, which lead to complex seepage characteristics. With the increased levels of oil exploration and development, it becomes essential to have an in-depth analysis of the problemsencountered in the development of tight sandstone reservoirscurrently, rational, scientific and efficient development way of tight sandstone reservoir. So it is urgent to carry out the research on the micro reservoir of tight sandstone and the characteristics of natural gas seepage.The research of microscopic pore throatsstructure of rock is the core content of reservoir microscopic study, because it is an essential factor affecting the reservoir reservoir storage and seepage capability, and the research of the distribution and flow conditions in a multiphase fluid reservoir has important guiding significance for the development of oil and gas fields.Su 14 well area is located in the south central area of Sulige gas field, at present, the relevant research is less in Sulige gas fieldSu 14 well area, so we take upper Paleozoic He8 and Shanl section of Su 14 well area as the the main research object,by using a large number of analytical laboratory data of an ordinary sheet, cast thin section, X diffraction, quantitative whole rock, field emission scanning electron microscopy, CT scan, high pressure mercury, mercury and so on, we conducted in-depth study of the Sulige gas field tight sandstone reservoir rock type, the microscopic pore throats structure and microscopic pore throats distribution, and have some correlation analysis with reservoir physical property, respectively. In addition, we analyze the distribution of gas and water and the characteristics of seepage flow by usingmicroscopic seepageexperiments and gas-water relative permeability experiments. The main achievements are as follows:(1) The data of high pressure mercury experimentalcan be used to statistical reservoir pore throats radius distribution and the contribution rate of pore throats to reservoir permeability in different radius,while permeability contribution rate can indirectly reflect the flow capacity in different scales pore throats. Experimental results show: Sulige tight sandstone reservoir is mainly composed of nanoscale pore throats (Pore throat radius<0.1μm) and submicron pore throats(0.1μm<Pore throat radius<1μm), the contribution rate of sub micron pore throats to reservoir permeability is the largest, with an average of 60.79%, followed micron pore throats(Pore throat radius≥1μm), the average contribution rate of 34.13%, the contribution rate of nano pore throats to reservoir permeability is very low, which mean the effect of micro pore throats and sub micron pore throats on the reservoir permeability is obvious, while the nano scale pore throat basically does not participate in the flow. Among them, type I reservoirsare mainly composed of sub micron pore throats and micron pore throats, micron pore throat plays the leading role in reservoir permeability, with the contribution rate up to 91.83%, sub micron grade pore throats and nano pore throats contribution to reservoir permeability of little; Type II reservoirs are mainly composed of sub micron pore throats and nano pore throats, and micro pore throatsmakethe largest contribution to reservoir permeability, followed by sub-micron pore throat; Type III reservoirsare mainly composed of nano pore throats and sub micron pore throats, the sub micron pore throatsbegin to play a leading role in reservoir permeability, the average contribution rate up to 88.83%; Type 4 reservoirs are mainly composed of nanoscale pore throats, micro pore throatsarerare, the sub micron pore throats play a leading role in the reservoir permeability.(2) The Sulige tight sandstone reservoirs can be divided into four major categories of Ⅰ~Ⅳ, as we take the reservoir physical property, the main rock types, pore types, seepage coefficient,the maximum pore throats radius, sorting coefficient, average roar radius, maximum roar radius, mainstream roar radius, unit volume rock effective throats volume, the size of average pore throats ratio and the distribution of pore throats as the basis for the classification.(3) Microscopic gas drive water experiments show:In the tight sandstone reservoir, during the process of accumulation, gas flow throughthe channel with large pore throat radius and good connectivitypreferentially,there is little gas in smallpore throats, until the displacement pressure increases to a certain degree, the gas began to enter the small pore throats;The water saturationof Sulige gas field is higher, the average value reach to 50%, which means the reservoir forming process is insufficient, and the reservoir is not sufficient, localreservoirs with good physical properties are easy to occur with high water content.(4) The new micro seepage experiment (gas pressure relief experiment) show.Under the same water saturation, the higher the physical properties of the reservoir are, the higher the degree of gas recovery in unit time, under the same physical property, the lower the water saturation is, the higher the degree of gas recovery is, the higher the reservoir permeability is, the stronger the carrying capacity of liquid is, and tight sandstone reservoirs all have a long low-pressure and low-yield stage, the lower the reservoir permeability is, or the higher the water saturation is, the longer the low-pressure and low-yield stage is.(5) The results of unsteady state gas drive water relative permeability experiment show that:In terms of relativelyconventional reservoirs, the irreducible water saturation (Swi), residual gas saturation (Sgr) and water saturation in the isotonic point (Sx) of tight sandstone are larger, while the gas relative permeability under irreducible water saturation (Krg(Swi)), the water relative permeability under residual gas saturation (Krw(Sgr)), the relative permeability in isotonic point (Krx(Sx)) and the gas water common infiltration area(S)of tight sandstone are smaller, and there exist a kind of water phase dominant relative permeability curve in tight sandstone; We put forward a quantitative classification scheme based on reservoir permeability (K), Krg(Swi), Krw(Sgr), Krx(Sx) and curve morphological characteristics, the tight sandstone gas-water relative permeability curves are divided into class Ⅰ~Ⅲ, the classification and the typesof gas well one one correspondence,and the overall compliance rate reached 89.7%. This classification can broaden the application of relative permeability curves and has important guiding significance to the actual production.
Keywords/Search Tags:tight sandstone, microscopic pore throat structure, phase permeability curve, micro seepage experiment, seepagecharacteristics
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