Study On Development Geology Characteristics Of Ordovician Reservoir In Well YB1Area, Tarim Basin

Maigaiti Slope is located in the western Tarim Basin, is a tectonic unit insouthwestern Tarim Basin. In recent years, the Northwest Oilfield branch companyincreased exploration efforts of this area. In2009November, it is obtained industrialoil flow according to the deployment of the Well YB1in third large acid fracturing inthe southeast of Maigaiti Slope, achieved a breakthrough in oil and gas exploration ofOrdovician carbonate rock in Yubei area. In2011, it has successively deployed5development evaluation wells in Well YB1area, has access to industrial productionand put into production.At present, because of little drilling date and the low degree of exploration anddevelopment in Yubei area, exploration development still exist many problemsincluding the reservoir type and distribution characteristics of unclear understanding,oil-water distribution unclearly and reservoir energy and oil well productivity ofcognition is not enough. This paper studies the principle and method of reservoirgeology, laboratory testing, reservoir geophysical logging, oil and gas developmentgeology and reservoir engineering, on the basis of previous structure, fracture andpalaeo-geomorphology research results, analyses reservoir space types and reservoirtypes using the core, drilling and well logging data; fully used the production well test,well logging and dynamic development data, analyses the oil-water distribution andthe types of reservoir; based on production performance of wells evaluate reservoirenergy and productivity of the favorable reservoir.Based on well core, logging, well logging (including imaging logging) andtesting data of19exploration and appraisal wells in study area, it show that the mainreservoir space types can be split into cracks, dissolved pores and large cave, in whichcrack and high angle middle-small cracks with different degree of filling are the main;dissolved pores is given priority to with small holes, calcite filling;YB1,YB1-1X,YB1-2and YB1-5wells are drilled in the caves. The drilling profilereservoir is divided into fractured, fractured cavern and karst cave type reservoir. Thecomprehensive identifiable symbols of fractured, fractured cavern and karst cave typereservoir are founded based on analyzing the characters of conventional logging and imaging logging response of the typical core crack, the cavern interval and ventleakage zone. Various types of reservoir intervals are classified in11single wells inthe study area on the longitudinal development, we then compiled single wellintegrated histogram and carried out comparative study of even well reservoirdevelopment section, which combined with exploration and seismic section. Currentlybuilded production wells could be given priority to with fractured cavern and karstcave, longitudinally be divided into three period of reservoir on preliminary.According to single well logging, testing and producing test data, it summarizeselectrical characteristics of the three types of reservoir including fractured, fracturedcavern and karst cave type reservoir, put forward electrical symbol of dividing oillayer and water layer, which apply to the single well section of oil-water layercomprehensive division. Reservoir resistivity is affected by formation fluid properties,reservoir types and lost circulation. No lost circulation, resistivity which consisted ofoil layer with fractured and fractured cavern type and water layer is demarcated by100.m and the caves in the lost circulation resistivity is generally less than100.m.When the reservoir in karst cave type position is low or be in poor condition, its flowback rate may high, we can’t put the initial water production simple due to water layeror oil-water producing layer.From the original single well oil-water distribution and development of oil-waterchanges, analyzed oil-water distribution characteristics of fracture cave reservoir;combined with fracture, palaeo-geomorphology and reservoir space developmentpredicted results, from fracture cavern reservoir formation and hydrocarbon charging,studied the control factors of oil-water distribution. In addition to the YB1-8at the topof the test water production, all the well profile located in Well YB1uplift fracture ofthe east high position rely mainly on oil; middle and low part of the YB1-1isdominated by water at the top. The testing well reservoir pressure declines quicklyand no-water production period is short, besides YB1-4well, each well has beenoutput formation water, the study area of oil and gas charging degree is not high as awhole. The reservoir in Well YB1area is fracture and karst, which determines themutual separation of reservoir space. Generally low energy of oil wells have differentdevelopment performance and earlier water breakthrough, it show that the reservoirspace take small localized fracture cave as the principal thing. Combined with theproperties of crude oil, formation pressure and temperature conditions, thecomprehensive reservoir characteristics of Ordovician reservoir in Well YB1Areacan be described as carbonate karst fractured cavern reservoir with normal temperature and pressure conditions of mid-heavy in unsaturated oil.Statistics show that wells in Well YB1Area productivity have a certainrelationship with seismic reflection characteristics and reservoir characteristics; whenthe main reservoir profile is fractured cavern type, it has a higher initial production;when the reservoir mainly is fractured, the general yield is low. Based on fracturecave reservoir development is mainly developed in the top surface of80m below onYingshan Formation, advised that the depth into the mountain is no more than100mand deploy development wells on the monopolic high position.