Lithofacies classification is one of the key modelling components in reservoir characterization. Log-facies classification methods aim to estimate a profile of facies at the well location based on the values of rock properties measured or computed in well log analysis (such as density, porosity, P-Wave, shale content and mineralogy). In this study, the classification of lithofacies was carried out in X field. The first step of classification lithofacies is cross-plot of each petrophysical data, the result of this step is used as a priori data to statistical facies classification (k-means algorithm). Lithofacies in this study were successfully separated into two facies namely sand and shale. The results obtained show that X Field is a gas saturated with sandstone as the main reservoir, especially in the Plover formation.
An initial subsurface survey to predict the aquifer is important to avoid the unprospect drill location and getting groundwater with the right discharge. In this study, prediction of the aquifer was carried out using the seismic refraction method in Jatimulyo Village, Jati Agung District, South Lampung Regency. The data was collected on October 6, 2019 using the SUMMIT X One seismic tool with 24 Geophones. The first break data from p-wave travel time is processed and interpreted using the Hagiwara method. Interpretation results show that there are three layers of subsurface lithology in the study area. The weathering layer was found at 2 m to 3.5 m depth with average velocity of 360 m/s. The second layer is dry sand with a velocity of 890 m/s at a depth of 2 m to 8 m. The third layer with a 2300 m/s velocity is a mixture of clay rock and saturated sand at depths of more than 8 m. As a comparison there is resistivity distribution data on the same measurement line in the study area. The overall interpretation shows that at a depth of 12 m with saturated clay sedimentary rock as a prospect of aquifer in this study area.
Abstrak -Pada eksplorasi hidrokarbon, kita membutuhkan suatu indikator yang menunjukkan keberadaan hidrokarbon secara akurat. Maka dari itu, dengan menggunakan indikator tersebut, kita dapat melihat sebaran serta dimensi dari reservoar hidrokarbon dengan lebih baik. Indikator yang digunakan pada penelitian kali ini adalah Faktor Dispersi Perubahan Kecepatan Gelombang P. Indikator ini akan melihat seberapa besar perubahan kecepatan gelombang P terhadap frekuensi. Pada media yang berpori dan tersaturasi gas, kecepatan gelombang P akan mengalami penurunan terhadap frekuensi yang disebabkan karena adanya atenuasi. Sehingga Faktor Dispersinya akan sangat bernilai negatif. Maka dari itu nilai Faktor Dispersi Perubahan Kecepatan Gelombang P sangat dipengaruhi oleh keberadaan gas pada pori batuan. Prediksi sebaran gas dengan menggunakan indikator Faktor Dispersi Perubahan Kecepatan Gelombang menunjukkan hasil akurat pada daerah yang terdapat sumur eksplorasi, dimana pada daerah tersebut menunjukkan keberadaan gas sesuai dengan apa yang diperlihatkan oleh data sumur. Maka dari itu, indikator Faktor Dispersi Perubahan Kecepatan Gelombang P merupakan indikator yang sensitif untuk melihat keberadaan hidrokarbon yang berupa gas.Abstract -In hydrocarbon exploration, we need an indicator that shows the presence of hydrocarbons accurately. Therefore, using the indicator, we can better see the distribution and dimensions of the hydrocarbon reservoir. The indicator used in this study is the P-Wave Difference Dispersion Factor. This indicator will see how much the P wave velocity changes with frequency. In porous and gas saturated media, the P wave velocity will decrease with frequency caused by attenuation. So the Dispersion Factor will be very negative. Therefore the value of P-Wave Difference Dispersion Factor is strongly influenced by the presence of gas in the rock pore. Gas distribution prediction using the P-Wave Difference Dispersion Factor shows accurate results in the area where there are exploration wells, which in the area indicate the presence of gas according to what is shown by the well data. Therefore, the indicator of P-Wave Difference Dispersion Factor are sensitive to the presence of hydrocarbon in the form of gas.
Sebagian warga yang tinggal di sekitar Dusun IID, Desa Jatimulyo, Kecamatan Jati Agung, Kabupaten Lampung Selatan; sering mengalami kekeringan air tanah pada sumur bor yang dimilikinya. Kedalaman sumur bor tersebut sekitar 10 meter, padahal ada sumur bor dengan kedalaman yang sama, kuantitas airnya banyak. Untuk mengatasi permasalahan ini, tim pengabdian kepada masyarakat menggunakan metode geolistrik untuk mengidentifikasi kemenerusan lapisan air tanah di dusun tersebut. Metode geolistrik 2 dimensi diaplikasikan di lokasi pengukuran agar dapat memberikan informasi persebaran nilai tahanan jenis listrik di area tersebut (secara horizontal dan vertical) sepanjang bentangan 210 meter dengan jarak antar elektroda sebesar 14 meter. Hasil pengolahan data menunjukkan bahwa lapisan air tanah di sekitar lokasi memiliki kuantitas air tanah yang berbeda, dilihat dari persebaran nilai resistivitasnya (tahanan jenis listrik). Informasi warga terkait kedalaman air tanah dan kuantitas air tanah, cocok dengan penampang resistivitas. Bagi warga yang tinggal di sebelah Barat, dapat memanfaatkan air tanah hanya dengan kedalaman sumur bor sekitar 10 meter. Namun, sebagai rekomendasi bagi warga di sebelah Timur, tim menyarankan untuk membuat sumur bor dengan kedalaman lebih dari 25 meter.
Detection of the presence of saturated hydrocarbons in pores or rock fractures is a major problem in the field of exploration geophysics which is interesting to study. Some of the fluid saturation indicators were originally derived from the Zoepprit equation. However, the indicator that is derived from the linearization of the reflection coefficient is not influenced by frequency. In fact, frequency is a physical quantity that is very sensitive to the presence of fluid in a pore or rock fracture. Seismic waves will experience attenuation and dispersion when propagating through a porous medium or gas-saturated fractures. Therefore, we need an indicator whose value is influenced by changes in the frequency of seismic waves. This indicator is an attribute of the velocity dispersion. In previous studies, the velocity dispersion attribute was used to detect the fluid content of gas in sandstone. Based on this research, it turns out that it shows effective results in mapping the presence of saturated gas zones in the carbonate pores. In the end, the results of this study will be able to map the presence of saturated gas zones in carbonate reservoir.
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