Penelitian ini bertujuan untuk menganalisis karakteristik reservoir karbonat pada Formasi Lower Baturaja di Cekungan Sunda menggunakan parameter petrofisika, distribusi fasies karbonat, serta analisis lingkungan pengendapan. Formasi Lower Baturaja dipilih karena memiliki potensi sebagai reservoir hidrokarbon yang signifikan, namun menghadapi tantangan heterogenitas batuan karbonat yang kompleks. Metodologi penelitian mencakup analisis petrofisika, elektrofasies, fasies, dan penentuan unit aliran hidrolik (Hydraulic Flow Unit, HFU) untuk mengevaluasi kualitas reservoir yang menggunakan data log dari 5 sumur di P1-P5 serta data core dan RCAL dari 3 sumur berupa P1,P2, dan P5. Berdasarkan hasil analisis elektrofasies, daerah penelitian memiliki pola cylindrical (smooth dan serrated), bell, dan funnel yang terdiri dari 7 kelompok rock type/HFU yang terdiri dari HFU-1 hingga HFU-7. Daerah penelitian terdiri dari tiga asosiasi fasies, yaitu AF3 (wave dominated-slope), AF1 (Platform Interior – Open Marine/Lagoon), dan AF2 (Platform-Margin Reefs). Berdasarkan hasil petrofisika, nilai rata-rata parameter petrofisika di seluruh sumur area penelitian, yaitu volume shale 0.29-0.32 v/v, porositas efektif 0.067-0.128 v/v, dan saturasi air 0.57-0.89 v/v. Zona hidrokarbon ditentukan berdasarkan nilai cut-off, yaitu volume shale ≤0.48 v/v, porositas ≥0.09 v/v, dan saturasi air (Sw) ≤0.71 v/v. Zona net pay di tiap sumur dari lapangan ini berupa P1 24.62 ft, P2 5.5 ft, P3 114.57 ft, P4 45 ft, P5 32 ft dengan total ketebalan zona hidrokarbon 221.69 ft. Reservoir terbaik dan paling produktif di lapangan "K" adalah reservoir di zona net pay yang termasuk dalam kelompok rock type HFU 5-7 yang terdiri dari elektrofasies tersusun atas batuan karbonat yang terbentuk di asosiasi fasies AF3 (wave dominated-slope).

---

This research aims to analyze the characteristics of carbonate reservoirs in the Lower Baturaja Formation in the Sunda Basin using petrophysical parameters, carbonate facies distribution, and depositional environment analysis. The Lower Baturaja Formation was selected due to its significant potential as a hydrocarbon reservoir, despite facing challenges from complex carbonate rock heterogeneity. The research methodology includes petrophysical analysis, electrofacies, facies, and hydraulic flow unit (HFU) determination to evaluate reservoir quality using log data from 5 wells (P1-P5) and core and RCAL data from 3 wells (P1, P2, and P5). Based on electrofacies analysis results, the study area exhibits cylindrical (smooth and serrated), bell, and funnel patterns consisting of 7 rock type/HFU groups from HFU-1 to HFU-7. The study area comprises three facies associations: AF3 (wave dominated-slope), AF1 (Platform Interior – Open Marine/Lagoon), and AF2 (Platform-Margin Reefs). Based on petrophysical results, the average petrophysical parameter values across all wells in the study area are: volume shale 0.29-0.32 v/v, effective porosity 0.067-0.128 v/v, and water saturation 0.57-0.89 v/v. Hydrocarbon zones were determined based on cut-off values: volume shale ≤0.48 v/v, porosity ≥0.09 v/v, and water saturation (Sw) ≤0.71 v/v. The net pay zones in each well are: P1 24.62 ft, P2 5.5 ft, P3 114.57 ft, P4 45 ft, P5 32 ft, with a total hydrocarbon zone thickness of 221.69 ft. The best and most productive reservoir in the "K" field is the reservoir in the net pay zone belonging to rock type group HFU 5-7, which consists of electrofacies composed of carbonate rocks formed in facies association AF3 (wave dominated-slope).