An Integrated Study On Shale Gas Reservoir Characterization,South Sumatra Basin,Indonesia

The gas industry starts to turn their attention to the unconventional gas reservoir,such as gas shale reservoir,It becomes a major exploration target because of the gas storage properties and potential for the large recoverable resource.In addition,the shale typically functions as both the source rock and as a reservoir also.On shale gas exploration,there are key factors important in determining the prospects for shale gas such as organic geochemistry,thermal maturity,mineralogy,natural fractures.The complexity of a review on the determine the shale gas prospect area makes the high risks in shale gas exploration.Comparable straight to the completeness of the data availability,the higher the cost will be incurred.Cost efficiency is also one of the considerations to explore.Complete data distribution requirements even with just the lack of data are challenging enough to minimize the risk.This study is a combination between the data from the laboratory,drilling,wireline well logs,and seismic and modeling to the analytical study of petrophysics,geochemistry,geomechanics,and geophysics parameter in Talang Akar Formation.An understanding of shale geochemistry,mineralogy,and geomechanics is very important to understand how the shale reservoir has the potential to reserve and produce when carried out stimulation.This study classifies shale based on organic richness,maturity,type,shale strengths,shale brittleness and clay content.The result of the petrophysical analysis in the research area is the interval porosity value of 3%–15%which is very good porosity for shale,water saturation value(Sw)equal to 0.04-0.59,and the value of shale content(Vsh)is 0.42-0.96.The limit on which the shale is assumed to be able to store and retain gas in an economical quantity,in this case,the minimum porosity value of potential shale of at less 4%(0.04),minimum water saturation value set 50%(0.5),and the value of shale content(Vsh)minimum 50%(0.5).Using the Rock-Eval Pyrolysis data in JML-1 and JML-2 wells,we found the TOC richness from 1.04 wt.%to 6.12 wt.%of TOC(these are good and excellent criteria).According to the van Krevelen diagram,we conclude that the shale formation analyzed in JML-1 and JML-2 wells have type II and III kerogen which indicates that the target zone contains mostly gas and gas/oil.From the analysis of maturity,we conclude that the organic matter in the shale formation has reached the early mature stage in the depth around 3100 m based on Tmax data(>435~οC)or vitrinite reflectance(Ro)data(above 0.6%).Total Organic Carbon(TOC)modeling was determined using Passey’s method,Multilinear Regression,and Neural network.The analysis of brittleness,in principle,gives a better understanding of the shale fractability.This is important in hydraulic fracturing in order to produce gas from shale.Shale brittleness depends on the brittle mineral content,such as quartz,calcite,and dolomite.This happens because when we input the XRD data to the Jarvie’s(2012),Wang and Gale(2009),and modification Wang and Gale(2009)equations,the clay minerals has the higher composition compared to quartz in all the samples.The results of this brittleness index(BI)calculation will be used later for the correction data in the brittleness index(BI)log modeling.The brittleness index(BI)calculation for the Talang Akar Formation based on 18 samples of cuttings gave a BI value of 0.75 to 1.00.The geophysical analysis is performed to transform the seismic data,which has a lateral resolution,into the organic geochemical data.This strategy is very helpful in mapping the potential of hydrocarbon shale laterally.In order to transform seismic data to organic geochemical data,we first applied the seismic inversion to produce the acoustic impedance(AI)section.Further,we did sensitivity analysis as a reference to define shale potential zones.These results are supported by calculation of simultaneous inversion,which showed low impedance values for shale gas zone between 6000–8500((m/s)*(g/cc)).South Sumatra Basin formed on Eocene-Recent age,some shale intervals in this basin have been proven to be source rock for several oil and gas fields in the vicinity,this condition makes the shale layers are attractive for the evolution of shale gas exploration.The biggest challenge in the improvement of shale gas reservoir in Indonesia is the lack of reference to shale gas fields that have been in production in Indonesia is still very rare.Currently,the variation in shale gas layer either vertically or laterally further increase the level of uncertainty in studying the shale gas.Talang Akar Formation(TAF)is a prospective formation to produce hydrocarbon in the South Sumatra Basin.The Talang Akar Formation consists of sandstones originating from plain delta,shale,silt,quartz sandstone,with claystone inserts carbonate,coal,and conglomerate in few locations.Contact between Talang Akar Formation with Lemat Formation is not aligned in the middle and on the edges of the basin may para conformable,while the contact between the Talang Akar Formation and Telisa Limestone members is conformable.