Case Study Well Test Analysis on Gas Well in Basement Granite Reservoir of South Sumatera

摘要

Analysing well test in Basement Granite Reservoir gives a unique pressure derivative response.The well is an exploration gas well in South Sumatera penetrating 3286 feet of Granite Basement; while the extensive fracture is found only for its 200 feet.The first approach is to review geological data; source rock,chronostratigraphy,migration,and depth structure; to get the sense of the hydrocarbon and reservoir shape model.Petrophysical log data is utilized to evaluate the fracture distribution,direction,and intensity.The flow behaviour of the well is analyzed mainly by pressure derivative type curve matching analyses.The petrophysics log interpretation indicates the existence of two fracture types; namely partial fracture and open fracture,which contain sweet gas hydrocarbon.The fractures show in the well test as fracture dominated flow as early as early time region which superimposes with the very small wellbore storage effect.This flow is followed by bilinear flow prior reaching the middle time region.Two porosity due to fracture is shown in the middle time region.The late period indicated constant pressure circle boundary.Two fracture types shown in the petrophysics log interpretation agrees with the well test interpretations,as far as two porosity well model.The constant pressure circle outer boundary indicated that the reservoir varies in its fracture distribution which effects the reservoir flow behaviour.In conclusion,the flow model of the well is infinite conductivity with two porosity pseudo steady state reservoir model and constant pressure circle boundary model.The reservoir pressure is 1962 Psia with permeability of 1.45 mD,fracture coefficient of 50 mD-ft,storativity of 0.51 and interporosity flow coefficient of 4.38×10-6 mD-ft,and also skin of-0.52.Performing well test analyses by including all data resources would give much better understanding the flow behaviour of reservoir fluid in the reservoir.Additional data of field fracture distribution would benefit future well drilling locations.