SEISMIC RESERVOIR CHARACTERIZATION BASED ON LITHO-SEISMIC CLASSIFICATION CONSTRAINED BY WELLS TO DETECT GAS-BEARING SANDS IN PECIKO MAIN ZONE, MAHAKAM DELTA

摘要

Simultaneous seismic inversions were performedrnusing PSTM (Pre-stack time migration) data in thernPeciko field, offshore Mahakam Delta. The studyrnconcentrated on the Peciko Main Zone (~3 kmrnburial depth) which is the main gas producingrninterval of the field. The main objectives of thisrnproject were to identify and map gas-bearing sands,rnand possibly to define new targets for futurerndevelopment wells. Until 2012, seismic data hadrnlittle contribution to well planning for this intervalrnsince their resolutions are poor and the seismicrnimages only show the thick packages of stackedrnreservoirs.rnA rock physics feasibility study showed a fairrnseparation between gas-bearing sands and otherrnfacies in P impedance versus Poisson’s ratio crossplotsrneven if large overlaps among different faciesrnwere still observed. Hence a pre-stack inversionrnproject was launched to produce a P Impedance (IP)rnand a Poisson’s Ratio (PR) cube to overcome somernof the limitations of the seismic data, and was thenrnfollowed by a litho-seismic classification process.rnLitho-seismic classification was computed from thernIP and PR cubes to give the probabilities ofrnlithologies such as sand, carbonate, and shale, basedrnon the cross-plots of P-impedance and Poisson’srnratio. One of the main challenges was to identify thernfluid content of reservoirs.rnThe burial of the Peciko Main zone is relativelyrndeep and the fluid sensitivity on rock properties isrnnot prominent. Thus in the IP and PR cross-plotrndomain, water and gas sands overlap each otherrnsignificantly. In order to overcome this difficulty,the reservoir lithologies were identified first usingrnlitho-seismic classification, and then the fluid logsrnof production wells were correlated with pseudosandrnvolumes to understand the fluid content. Thernresults discovered several new targets where there isrnno well control and the seismic amplitudes didn’trnshow any distinctive characteristics.