Penentuan Top Overpressure dan Mekanisme Penyebabnya, Grup Balikpapan, Lapangan 'NUR', Cekungan Kutai, Kalimantan Timur

Istiqomah Nur Priyono, Ir. Jarot Setyowiyoto, M.Sc., Ph.D., IPU, ASEAN Eng.; Dr. Sarju Winardi, S.T., M.T.

2026 | Skripsi | TEKNIK GEOLOGI

Overpressure merupakan kondisi tekanan pori yang melebihi tekanan hidrostatik dan dapat meningkatkan risiko pemboran, seperti kick dan blowout. Penelitian ini bertujuan untuk menentukan profil tekanan pori dan kedalaman top overpressure serta mengidentifikasi mekanisme penyebab overpressure di Grup Balikpapan, Lapangan ‘NUR’, Cekungan Kutai. Penelitian dilakukan pada 12 sumur menggunakan data wireline log, data tekanan, Leak-off Test (LOT), drilling report, dan mudlog. Prediksi tekanan pori dilakukan menggunakan Metode Eaton dan Bowers, sedangkan tekanan rekahan dihitung menggunakan Metode Matthews dan Kelly serta divalidasi dengan data LOT. Hasil perhitungan kemudian diintegrasikan dengan data pemboran dan dikorelasikan berdasarkan struktur geologi untuk menentukan persebaran top overpressure. Analisis mekanisme dilakukan berdasarkan karakteristik profil tekanan, perubahan effective stress, serta crossplot sonik dan densitas. Hasil penelitian menunjukkan bahwa sumur-sumur yang mengalami overpressure memiliki zona hidrostatik normal dan transition overpressure, sedangkan hard overpressure hanya berkembang pada Sumur NUR-001. Top overpressure berada pada kedalaman 5840 ftMD/5570 ftTVDSS – 7813 ftMD/7524 ftTVDSS dan persebarannya mengikuti geometri struktur sinklin. Mekanisme utama pembentukan overpressure adalah loading berupa disequilibrium compaction yang berkembang pada seluruh sumur overpressure dan berkaitan dengan laju sedimentasi Grup Balikpapan yang tinggi. Mekanisme unloading berupa clay diagenesis teridentifikasi pada Sumur NUR-001 pada kedalaman 8000 ftMD/7937 ftTVDSS – 9000 ftMD/8937 ftTVDSS, khususnya pada interval hard overpressure.

Overpressure is a condition in which pore pressure exceeds hydrostatic pressure and can increase drilling risks, such as kick and blowout. This study aims to determine the pore pressure profile and top overpressure depth, as well as to identify the mechanisms causing overpressure in the Balikpapan Group, ‘NUR’ Field, Kutai Basin. The study was conducted using data from 12 wells, including wireline logs, pressure data, Leak-off Test (LOT), drilling reports, and mudlogs. Pore pressure was predicted using the Eaton and Bowers methods, while fracture pressure was calculated using the Matthews and Kelly method and validated  using LOT data. The calculated results were then integrated with drilling data and correlated with the geological structure to determine the distribution of top overpressure. The mechanisms were analyzed based on pressure profile characteristics, changes in effective stress, and sonic-density crossplots. The results show that the wells experiencing overpressure have normal hydrostatic and transition overpressure zones, while hard overpressure only occurs in Well NUR-001. The top overpressure occurs at a depth of 5840 ftMD/5570 ftTVDSS – 7813 ftMD/7524 ftTVDSS and its distribution follows the geometry of the syncline structure. The main mechanism responsible for overpressure is loading through disequilibrium compaction, which occurs in all overpressure wells and is related to the high sedimentation rate of the Balikpapan Group. An unloading mechanism caused by clay diagenesis was identified in Well NUR-001 at a depth of 8000 ftMD/7937 ftTVDSS – 9000 ftMD/8937 ftTVDSS, particularly within the hard overpressure interval.

Kata Kunci : Overpressure, Top Overpressure, Tekanan Pori, Tekanan Rekahan, Grup Balikpapan, Cekungan Kutai.