Study On Gas Log Interpretation And Gas Water Distribution Characteristics In Sebei Ⅱ Gas Field

This paper focus on Sebei Ⅱ gas field as the study area, integrate geology, well logging,test, production and dynamic data, to study the four behaviors relationship of reservoir,reservoir parameters, reservoir classification and identification, origin and distribution of lowresistivity formation, gas reservoir types and gas-water relation. The main concludes are asfollows:On the basis of studying the four behaviors relationship of reservoir and reservoirparameters, combining the reservoir geology, gas test, dynamic and production data of thestudy area, we discovered that the reservoir can be divided into three different types ofdistinct electrical characteristics and it’s hard to identify gas due to the change of shale andcarbonate content. The three main categories include:①conventional gas reservoir of highAC and coefficient of resistivity increases, low neutron porosity;②gas reservoir with low ACand neutron porosity, high coefficient of resistivity increases caused by high carbonate content;③gas reservoir with high AC, low neutron porosity, resistivity and coefficient of resistivityincreases caused by high formation water salinity and high mud content background.According to the characteristics of three types of gas reservoirs, good recognition effect wasachieved by the comprehensive method of "difference between interval transit time porosityand neutron porosity&coefficient of resistivity increases". Horizontal and vertical distributioncharacteristics of the gas reservoir are studied furthermore. The distribution on the plane ismainly controlled by the structure,the longitudinal distribution is primarily affected by thesedimentary evolution.Studies suggest that the low resistivity gas reservoir are mainly formed for the reason ofhigh bound water saturation, high formation water salinity, incomplete air waterdifferentiation by flat structural amplitude and the local enrichment of conductive minerals.SebeiⅡ gas field is deemed as anticline type layered gas reservoir with non-unified gasoil contact. Gas distribution is controlled by the structure, hydrodynamic force and lithology.Dry layers exist due to lithology changes in some non-major gas reservoir; Gas oil contactexhibits as higher in the south than in the north under the influence of stronger in the souththan in the north water system in the Qaidam Basin. The height difference mainly concentrated in between10m-25m, with an average of12.1m. Edge water is the main type offormation water in Sebei Ⅱ gas field; In the longitudinal direction there are some interbeddedwater layers which are difficult to gather gas due to poor capping conditions. There also existsome free water which is difficult to be replaced by gas in the gas reservoirs with poor porestructure because of high shale or carbonate content. There are four causes of reservoir boundwater, including clay adsorption, pore corner, micropore and gas streaming around.