1D GEOMECHANICAL MODEL FOR WELLBORE STABILITY AT NSK FIELD, CENTRAL SUMATRA BASIN, RIAU, INDONESIA.

• Main Author: Maria Angela, Vanessa
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/70196
• Institution: Institut Teknologi Bandung

NSK Field is one of the oil fields within the contractors cooperation area (PSC) of PT Chevron Pacific Indonesia, that is located in Rokan Block and one of the heavy oil producers in the Central Sumatra Basin. The geological structure of NSK field is an anticline that extends north ? south and northeast ? southwest. The eastern part of this field is bounded by a strike slip fault, and is divided into northern and southern areas separated by saddle and fault structures. The NSK field has the majority of reserves remaining in the Duri Formation, while minorities are in Bekasap Formation, Bangko and Menggala. This study discusses the one dimensional geomechanics model on wells located in NSK Field in order to know the condition of in-situ stresses that will affect the stability of the boreholes in NSK Field. The one-dimensional geomechanics model consists of five components, namely in-situ principal stress which are SHmax = S1, Sv = S2 and Shmin = S3 (where it is consisted of a magnitude and a direction), pore pressure, elastic properties and rock strength. Based on geomechanical model from this research, the current stress regime in NSK field is in strike-slip regime condition with S1 > S2 > S3. Vertical stress (Sv) gradient has a value range between 0.77–0.93 psi//ft, minimum horizontal stress (Shmin) = 0.69–0.80 psi//ft and maximum horizontal stress (SHmax) = 0.86–1.17 psi/ft. In wellbore NSK-86, the maximum horizontal stress gradient ranges between 23 ? 26 ppg or 1.19-1.35 psi/ft. The direction of maximum horizontal stress is in NE–SW and minimum horizontal stress is in NW–SE. Wellbore stability analysis indicates that the safe or acceptable mud weight is 11.33 ppg from the top depth of data to top of Duri B (Duri Formation), 10.77 ppg in Duri B to the top of Duri C (Duri Formation), 9.46 ppg in Duri C to the top of Duri D (Duri Formation), 7.98 ppg in Duri D to the top of Bekasap Formation, and lastly, 7.14 ppg in Bekasap Formation to the bottom depth of data.