Analisis anomali resistivitas dan pengaruhnya dalam perhitungan Sw berdasarkan interpretasi log pada lapangan X
S Salah satu permasalahan yang terjadi adalah ketika menganalisis hasilrekaman logging adalah ditemukannya anomali pada hasil pembacaan tersebutbaik dari faktor lingkungan maupun dari Logging Tools itu sendiri.Pada lapangan X terdapat lima sumur yang diteliti, yaitu sumur X-05, X-06, X-07, X-17 dan X-25. Pada kelima sumur tersebut ditemukan adanya anomalipada Resistivity Log. Anomali Resistivity Log yang terjadi antara lain LowResistivity Contrast pada zona hidrokarbon yaitu terjadinya perbedaan hasil antara resistivitas pada zona deep dan zona shallow yang tidak terlalu signifikan dan terjadi High Resistivity – Low Contrast pada Water Bearing Zone yang ada pada kelima sumur di lapangan X, yaitu terjadinya pembacaan resistivitas yang tinggi tetapi dengan kontras resistivitas antara resistivitas pada zona deep dan zona shallow yang tidak terlalu signifikan. Untuk sumur X-05, Low Resistivity Contrast berada pada kedalaman 1263-1312 feet, dan High Resistivity – Low Contrast berada pada kedalaman 1323-1381 feet. Untuk sumur X-06, Low Resistivity Contrast berada pada kedalaman 1244.5-1284 feet, dan High Resistivity – Low Contrast berada pada kedalaman 1284.5-1320 feet. Untuk sumur X-07, Low Resistivity Contrast berada pada kedalaman 1248-1289 feet, dan High Resistivity – Low Contrast berada pada kedalaman 1290-1362 feet. Untuk sumur X-17, Low Resistivity Contrast berada pada kedalaman 1166-1233 feet dan 1286-1330 feet, dan High Resistivity – Low Contrast berada pada kedalaman 1233-1286 feet. Untuk sumur X-25, Low Resistivity Contrast berada pada kedalaman 1175-1273 feet, dan High Resistivity – Low Contrast berada pada kedalaman 1281-1360 feet. Setelah dilakukan analisis kualitatif pada setiap sumur di lapangan X, maka dilakukan analisis kuantitatif pada setiap sumur tersebut, yaitu perhitungan Volume Shale Rata-Rata, Porositas Efektif Rata-Rata, Resistivitas Air Formasi, dan Saturasi Air Formasi Rata-Rata. Kemudian dilakukan perhitungan Volume Shale rata-rata, dan diperoleh nilai Volume Shale rata-rata dari setiap sumur pada zona prospek hidrokarbon X-05, X-06, X-07, X-17dan X-25 yaitu 21.75%, 21.29%, 16.58%, 43.43% dan34.45%, dan 17.82%. Pada Water Bearing Zone didapat nilai Volume Shale rata-rata dari sumur X-05, X-06, X-07, X-17 dan X-25 yaitu 20.99%, 21.78%, 40.16%, 48.56% dan 37.31%. Setelah dilakukan perhitungan Porositas Efektif rata-rata, didapat nilai dari setiap sumur pada zona prospek hidrokarbon sumur X-05, X-06, X-07, X-17 dan X-25, yaitu 18.73%, 21.02%, 23.31%, 16.85% dan 25.23%, dan 23.94%. Pada Water Bearing Zone sumur X-05, X-06, X-07, X-17 dan X-25 didapat nilai Porositas Efektif rata-rata yaitu 23.28%, 24.14%, 20.21%, 25.23%,dan 21.05%. Untuk menentukan harga Resistivitas Air Formasi Water Bearing Zone digunakan Metode SP Log, dimana diperoleh hasil untuk sumur X-05, X-06, X-07, X-17 dan X-25 sebesar 4.1 Ωm, 3.76 Ωm, 3.11 Ωm, 3.4 Ωm, dan 3.48 Ωm.Sedangkan nilai Resistivitas air formasi pada zona hidrokarbon untuk sumur X-05, X-06, X-07, X-17 dan X-25 sebesar 1.3 Ωm, 1.1 Ωm, 0.9 Ωm, 1.4 Ωm dan 2Ωm, dan 2.5 Ωm. Nilai Salinitas Air Formasi pada sumur X-05, X-06, X-07, X-17dan X-25 pada Temperatur Formasi sebesar 120°F yaitu 800 ppm, 900 ppm, 1700 ppm, 1000 ppm dan 1000 ppm. Nilai ini didapat dengan menggunakan Chart Gen-9. Hal ini membuktikan bahwa Water Bearing Zone pada lapangan Xmemiliki air formasi Fresh Water. Metode Rwa juga digunakan untuk menentukan nilai Resistivitas Air Formasi pada lapangan X, dimana nilai untuk masing-masing sumur X-05, X-06, X-07, X-17 dan X-25 adalah 8.83 Ωm, 19.68 Ωm, 20.11 Ωm, 16.37 Ωm dan 19.8 Ωm. Untuk nilai resisivitas air formasi dengan metode Rwa pada zona hidrokarbon di sumur X-05, X-06, X-07, X-17 dan X-25 adalah 2.4 Ωm, 3.36 Ωm, 1.296 Ωm, 1.408 Ωm dan 1.782 Ωm, dan 1.51 Ωm. Setelah dilakukan perhitungan, maka didapat nilai Saturasi Air Formasidari kedalaman setiap sumur yang merupakan zona prospek hidrokarbon padasumur X-05, X-06, X-07, X-17 dan X-25 dengan metode SP Log yaitu 46.6%,46.7%, 30.71%, 34.82% dan 36.12%, dan 35.64%. dan nilai Saturasi Air Formasipada zona prospek hidrokarbon di sumur X-05, X-06, X-07, X-17 dan X-25 dengan menggunakan metode Rwa yaitu 51.5%, 65.86%, 62%, 40.3% dan 54.54%, dan 57.05%. Untuk perhitungan Saturasi Air Formasi pada Water Bearing Zone dengan nilai Rw yang didapat dengan metode SP Log, didapatkan nilai masing-masing Saturasi Air Formasi Rata-rata pada sumur X-05, X-06, X-07, X-17 dan X-25 yaitu 67.3%, 47.9%, 49.92%, 50.4%, dan 51.77%. Untuk nilai Saturasi AirFormasi rata-rata dengan menggunakan nilai Resistivitas Air Formasi denganmetode Rwa pada sumur X-05, X-06, X-07, X-17 dan X-25 adalah 93.24%,93.26%, 93.61%, 83.32%, dan 96.08%. Berdasarkan dari hasil perhitungan yang telah dilakukan, maka metode Rwa lebih cocok untuk digunakan, dikarenakan nilai Saturasi Air Formasi yang lebih valid untuk setiap sumur dan zona pada lapangan X.
O One of the problems that could happened when analising the log reading isthe findings of anomalies in the reading itself. Whether from the environemtalfactor or even the logging tools itself. There are 5 wells available on field X to be analysed, there are X-05, X- 06, X-07, X-17 and X-25 well. There are Resistivity Log anomalies found Inside these wells. The anomalies found there are Low-Resistivity Contrast on the hydrocarbon zone where the difference between Deep Resistivity and Shallow Resistivity Readings are not very significant. And also the High Resistivity – Low Contrast Formation on the Water Bearing Zone that is available on the whole 5 wells available, where the formation have problem with the high resistivity reading but the contrast between the Deep Resistivity and Shallow Resistivity are not very significant. For the X-05 well, Low Resistivity Contrast happened on 1263-1312 feet, and High Resistivity – Low Contrast happened on 1323-1381 feet. Then for the X- 06 well, Low Resistivity Contrast happened on 1244.5-1284 feet, and High Resistivity – Low Contrast happened on 1284.5-1320 feet. Next for X-07 well, Low Resistivity Contrast happened on 1248-1289 feet, and High Resistivity – Low Contrast happened on 1290-1362 feet. For X-17 well, Low Resistivity Contrast happened on 1166-1233 feet and 1286-1330 feet, and High Resistivity – Low Contrast happened on 1233-1286 feet. And the last one for well X-25, Low Resistivity Contrast happened on 1175-1273 feet, and High Resistivity – Low Contrast happened on 1281-1360 feet. After the qualitative analysis done on each wells on field X, the next thing to be done is doing the quantitative analysis for every wells, that includes the calculation of average shale volume, average effective porosity, formation water resistivity, and the average water saturation. After the average shale volume calculated, the result of average shale volume on each wells that are identified as the hydrocarbon zone, there are 21.75% on X-05 well, 21.29% on X-06 well, 16.58% on X-07 well, 43.43% and 34.45% on X-17 well, and the last is 17.82% on X-25 well. And for the each wells that are identified as the water bearing zone on field X, the result of average shale volume are 20.99% on X-05 well, 21.78% on X-06 well, 40.16% on X-07 well, 48.56% on X-17 well, and the last one is 37.31% on X-25 well. And then after the calculation of average shale volume, the next one is the calculation of average effective porosity, the result of the average effective porosity on each wells that are identified as the hydrocarbon zone are 18.73% on X-05 well, 21.02% on X-06 well, 23.31% on X-07 well, 16.85% and 25.23% on X-17 well, and the last one is 23.94% on X-25 well. And then on the zones that are identified as the water bearing zone, the result of the effective average porosity on each wells are 23.28% on X-05 well, 24.14% on X-06 well, 20.21% on X-07 well, 25.23% on X-17 well, and the last one is 21.05% on X-25 well. For the calculation of water formation resistivity on the zones that are identified as water bearing zone, the method used is SP Log method, the results on X-05, X-06, X-07, and X-25 well are 4.1 Ωm, 3.76 Ωm, 3.11 Ωm, 3.4 Ωm, and 3.48 Ωm. And then for the hydrocarbon zones, the value of water formation resistvity for each X-05, X-06, X-07, X-17 and X-25 well are 1.3 Ωm, 1.1 Ωm, 0.9 Ωm, 1.4 Ωm and 2 Ωm, and 2.5 Ωm. The value of Formation Water Salinity on X-05, X-06, X-07, X-17 and X-25 well at 120°F Formation Temperature is 800 ppm, 900 ppm, 1700 ppm, 1000ppm and 1000 ppm. The value is obtnaied by using Gen-9 Chart. This resultconcludes that Water Bearing Zone on Field X Fresh Water Type WaterFormation. Rwa method is also used to determine the value of Formation WaterResistivity on field X, where the value of each X-05, X-06, X-07, X-17 and X-25wells are 8.83 Ωm, 19.68 Ωm, 20.11 Ωm, 16.37 Ωm and 19.8 Ωm. For theFormation Water Resistivity by using Rwa method of hydrocarbon zones on X-05, X-06, X-07, X-17 and X-25 wells are 2.4 Ωm, 3.36 Ωm, 1.296 Ωm, 1.408 Ωmand 1.782 Ωm, and 1.51 Ωm. After the calculation is done, then the value of Formation Water Saturation obtained from each hydrocarbon zones on well X-05, X-06, X-07, X-17 and X-25 by using SP Log method are 46.6%, 46.7%, 30.71%, 34.82% and 36.12%, and 35.64%. and the value of Formation Water Saturation of hydrocarbon zones on X- 05, X-06, X-07, X-17 and X-25 well by using Rwa method are 51.5%, 65.86%, 62%, 40.3% and 54.54%, and 57.05%. For the calculation of Formation Water Saturation of Water Bearing Zone by using SP Log method, the value of each Formation Water Saturation on X-05, X-06, X-07, X-17 and X-25 wells are 67.3%, 47.9%, 49.92%, 50.4%, and 51.77%. For the value of Formation Water Saturation by using Rwa method, the value on X-05, X-06, X-07, X-17 and X-25 wells are 93.24%, 93.26%, 93.61%, 83.32%, and 96.08%. And based on the calculations done, then the Rwa method is more suitable to use, because the validity of the Formation Water Saturation values obtained from the whole zones and wells on field X.