Production Log Interpretation through A Slotted Liner during Cold Water Injection: Integration with Electrical Borehole Images in a High Temperature Geothermal Development Well, South Sumatra, Indonesia Authors: Richard E. Netherwood*, Dibyatanu Kundu**, Aditi Pal**, Mega Ardhiani Puspa**, M. Yustin Kamah***, Dratjat Budi Hartanto***, M. Husni Thamrin*** * Communicating author. PT Schlumberger Geophysics Nusantara, 17 th Floor, Sentra Mulia, Jl H.R. Rasuna Said Kav X-6 No.8, Jakarta 12940, Indonesia (Telephone: +62 21 5227050, Fax: +62 21 2500364, e-mail: netherwood@slb.com) ** PT Schlumberger Geophysics Nusantara, 17 th Floor, Sentra Mulia, Jl H.R. Rasuna Said Kav X-6 No.8, Jakarta 12940, Indonesia (Telephone: +62 21 5227050, Fax: +62 21 2500364, e-mail: kundu@jakarta.oilfield.slb.com, apal@jakarta.oilfield.slb.com, mpuspa@jakarta.oilfield.slb.com) *** PT Pertamina Geothermal Energy, Menara Cakrawali Lantai 15, Jl M.H. Thamrin, Jakarta Pusat No.9, Jakarta, Indonesia (Telephone: +62 21 39833222, Fax: +62 21 39833230, e-mail: yustinkamah@pgindonesia.com, dradjat@pgeindonesia.com, thamrin@pgindonesia.com) ABSTRACT Borehole electrical resistivity images and cased-hole production logs were acquired over two intervals of volcaniclastic sediments in a geothermal development well. The imaging tool was logged in the open wellbore; production log data were acquired inside a slotted liner. Cold water was injected during acquisition in order to cool the tools. The image log identified abundant conductive (open) fractures that are concentrated in, but not restricted to, more resistive (brittle) rock. Resistive (healed) fractures are less extensively developed. A number of faults were identified. Fractures and faults strike mainly NNW-SSE / NW-SE, corresponding to the maximum horizontal stress direction determined from drilling induced fractures. These orientations are to be used to optimize future well design and development strategy. Production logging identified a number of potential steam production zones where water was either injected into or flowed out of the formation at 1,100 m, 1,546-1,554 m, 1,660-1,780 m, 1,917 m and 2,170-2,260 m (TD). These potential production zones are associated with specific geological features, including faults, isolated large fractures and fracture zones. INTRODUCTION It is important to characterize fracture systems in geothermal reservoirs in order to determine producible zones and to provide invaluable data for mapping fracture systems on a fieldwide scale. Standard logging tools are generally rated to only 250 o C and, rely on the borehole being filled with liquid. Steam-filled geothermal wells with reservoir temperatures in excess of 250 o C cannot be logged on wireline while flowing. In this case study a borehole resistivity imaging tool and a production log, including spinner, temperature, pressure and fluid density, were logged over two intervals of volcaniclastic sediments (2271-1880m and 1869-880m) during injection of cold water into a geothermal development well drilled in Jambi Province, South Sumatra, Indonesia (Figure 1). The borehole imaging tool was logged in the open wellbore in order to identify, characterise and orientate fractures and other planar geological features that cross the borehole. Production log data were acquired through a slotted liner and were integrated with the open-hole caliper and image log data. The borehole imaging tool employed has 192 electrical sensors mounted on 8 pads on a lower sonde (Figure 2). An electrical current is injected into the formation from an upper electrode. The return current entering the lower sensors is measured and is proportional to the resistivity of the formation in front of the recording sensor. The 192 resistivity readings are normalized and colour scaled into 164 colour bins, ranging from white, representing the most resistive formation encountered in the logging run, through yellow, orange, brown to black, representing the most conductive formation encountered. The resulting resistivity image has a resolution of 0.2 inch / 5 mm, with 64 % coverage in 12.25 inch and 80 % coverage in 8.5 inch borehole diameters. The imaging tool also records two orthogonal borehole calliper measurements.