ALTERNATIF INTERPRETASI LEAK OFF TEST UNTUK ANALISIS GEOMEKANIKA PADA TATANAN TEKTONIK FOLD THRUST BELT STUDI KASUS CEKUNGAN BANGGAI

• Main Author: Farissa Nabilah, Suci
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/75627
• Institution: Institut Teknologi Bandung

<p align="justify">The results of the leak-off test provide a stress response below the surface. Two possibilities that can occur are tensile fracture and shear fracture. Based on the classic interpretation from Hubbert and Willis (1957), if a tensile fracture occurs, then the orientation is parallel to the minimum stress (S3) so that S3 = Shmin or S3 = Sv. Couzens-Schultz and Chan (2010) argue that the rock failure that occurs is not always tensile because it depends on the differential stress under the conditions, if the stress differential is small in general, a tensile fracture may be formed, but if the stress differential is large then contraction may occur. This study demonstrates this argument in the Banggai Basin because so far existing geomechanical studies have stated that the stress regime is normal (Sv > SHmax > Shmin), even though neotectonic conditions show the influence of horizontal compressional forces both from the evidence of the tectonic setting which is the fold thrust belt, the focal mechanism of the earthquake up, a gradient structure on the subsurface. With the subsurface evidence of the Banggai Basin, this study shows that the rock characteristics in this basin have anisotropy and weak planes such as shearing, fractures, and secondary porosity in carbonate reservoirs associated with weak rocks. Thus, the origin of the Mohr Coulomb failure function is zero (So = 0). The consequence is that tensile fracture will never occur no matter what injection is made. This study argues that the stress response recorded in the leak-off test is a shear failure and the LOP pressure (leak-off pressure) is not the minimum stress (S3) so that it cannot be directly used as an in situ stress value as in the classical interpretation but rather the amount of injection required to create the shear fracture. The results of Banggai Basin stress regime analysis obtained are an increasing stress regime (SHmax > Shmin > Sv) with a gradient of SHmax of 35 MPa/km as the maximum stress and Sv as the minimum stress and has a large stress differential. This results in a good agreement between the geomechanical analysis of the well and the current deformation.