The separation process of lithology and fluid reservoir is an important part in the characterization of reservoir. It will explain the physical properties of reservoir rock lithology and fluid content by integrating the geophysics and petrophysical data. This process is difficult to do in the field "B" by using parameters of acoustic impedance and lambda mu rho (LMR), because it still has a fairly high degree of ambiguity. Poisson impedance (PI) has been implemented as a solution to address the problem. In cross-plot between Acoustic Impedance (AI) and Shear Impedance (SI), a rotation of both axes was conducted according to the trend of lithology-fluid to satisfy the equation of PI = AI – cSI. To improve the accuracy of PI calculation, the value of c (optimization factor of rotation) was calculated through the method of TCCA (Target Correlation Coefficient Analysis). The correlation with to be predicted wells data then be done. Analysis of sensitivity parameter was performed on two wells in the field "B". Parameters Zp, Zs and density which obtained from the simultaneous inversion then transformed into PI. PI models clearly showed the separation of rock lithology of hydrocarbon reservoir. Lithology impedance (LI) as a result of the PI-GR correlation was able to separate sand and shale very well. Similarly, the impedance Fluid (FI) as a result of PI-SW correlation was also able to separate the water content in the reservoir with high SW value relative to gas with a low value of SW. Hydrocarbon zone proven at 2360-2400 m. The slicing result of the volumes of Poisson impedance inversion has provided a clear distribution and interpretation of lithology and fluid content reservoir at the field "B" of South Sumatera.
The sandstone reservoir in the “OA” Field is situated in the Northern Bonaparte Basin, which is gas-saturated sandstone. Mineral diagenesis is also causing several reservoir zone areas to become tight sand. The inversion method using acoustic impedance (AI) is less sensitive in distinguishing sandstone and clay rock lithology since they have almost the same impedance. Simultaneous Inversion overcomes this problem by simultaneously inversing partial angle data (near, mid, far) to obtain physical parameters besides acoustic impedance which are expected to be more sensitive in distinguishing lithology and predicting the presence of gas fluids such as shear impedance (SI) and density. These three parameters can be derived as Lame (LMR) parameters. Cross plot analysis shows sensitive physical parameters to predict the distribution of lithology and the presence of gas fluid. Density sensitive in distinguishing lithology which is then inverted, obtaining sandstone cutoff values are 2.3-2.5 (g/cc), tight sand with cutoff 2.5-2.625 (g/cc) and clay stones with cutoff 2.625-2.8 (g/cc). The presence of gas fluid is predicted by inversing the parameter Vp/Vs
which has a cutoff of >1.6 and Lambda-rho cutoff of >25 (Gpa)*(g/cc). Analysis of the parameter distribution map shows the distribution of sandstones and the presence of dominant gas fluids in the northern area of the research zone with relatively clean sandstone, compared to relatively more southern regions.
Lapangan RB termasuk wilayah kerja blok Rangkas yang berlokasi di propinsi Banten memiliki Petroleum System yang sudah terbukti menghasilkan hidrokarbon. Di beberapa tempat terdapat rembesan minyak tetapi masih belum ada kajian yang mendalam mengenai potensi batuan reservoir penghasil hidrokarbon tersebut. Studi ini dilakukan untuk menentukan jenis litologi pada formasi Saraweh berumur Miocene awal dan formasi Cijengkol berumur Oligocene akhir-Miocene awal yang dijadikan sebagai kandidat batuan reservoir dengan melakukan perhitungan nilai impedansi akustik dan porositasnya. Nilai impedansi akustik tersebut dicrossplotkan terhadap parameter litologi gamma ray sebagai indikator litologi. Nilai porositas batuan dihitung berdasarkan hubungan empirik antara nilai impedansi akustik dan neutron-porosity. Hasil penelitian ini menunjukkan bahwa batuan karbonat memiliki nilai impedansi akustik berkisar antara 10000 ((m/s)*(g/cm³)) - 13500 ((m/s)*(g/cm ³)) dan nilai porositas kurang dari 0.20 v/v sedangkan batupasir memiliki nilai impedansi akustik berkisar antara 3500 ((m/s)*(g/cm³)) - 8000 ((m/s)*(g/ cm³)) dan nilai porositas 0.30 v/v-0.38 v/v. Nilai porositas yang dimiliki batupasir cukup baik sehingga dapat dijadikan sebagai kandidat batuan reservoir. Berdasarkan penampang impedansi akustik dan porositas, distribusi reservoir batupasir pada umumnya berkembang dan menebal ke arah utara dan timur sehingga pada area tersebut dapat dilakukan kegiatan eksplorasi lebih lanjut.
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