Mizoram Fold-thrust Belt, NE India: Initial Hydrocarbon Exploration Strategy Based on Balanced Strucutral Cross Sections

Borthakur, Ajoya N.; Changmai, Diganta; Mukhopadhyay, Dilip K.

The Tripura-Cachar-Mizoram areas in NE India and in adjoining areas of Bangladesh and Myanmar show a series of approximately N-S trending anticlines. Many of the anticlines are hundreds of km long and are spectacularly seen in regional satellite imagery-based DEM of NE India. Hydrocarbon systems in the NE India are mostly controlled by structural geometry formed during collision between the Indian and West Burmese plates in the late Mesozoic. Following Elliot's bow-and-arrow rule, the arcuate map pattern of the anticlines suggests an east-west collision and tectonic transport from east towards west. Although there are many producing oil/gas fields the NE Indian tectonic province, exploration efforts in the state of Mizoram have started recently. Recent geological/structural mapping and reflection seismic surveys in the remote and heavily forested hilly areas of Mizoram still do not permit definitive structural interpretations. In order devise an exploration strategy, including locations of first set of drilling, with minimum risk, the techniques of cross-section balancing have been applied. Balanced structural cross sections are essentially inverse structural modeling based on kinematics of fault-fold relations.

Out of sixteen anticlines present within the Mizoram exploration block, four anticlines and intervening synclines have been taken up for this stud. The anticlines are named as Tuahzawl. Aibwak, Seling and Keifang anticlines. The dip domain data suggest that the anticlines are fairly tight, sub-horizontal, upright, and sharp-crested, except for Keifang anticline, which is flat-crested. Six different kinematically valid balanced cross sections could be constructed using the same data set. Structural models used include parallel and similar folding above a decollement surface, forward-breaking detachment folding and ramp anticlines, such as fault-bend/fault-propagation folding, with breakthrough structures and with or without simple shear. Multiple valid balanced cross sections with the same data set do not render the technique untenable; rather it helps in better risk assessment of hydrocarbon exploration. Multiple valid structural models suggest that the strategy of drilling at the crest of anticlines except for Keifang anticline is not a sound proposition and deviated drilling from eastern limbs of the anticlines offers minimum risk. Detailed structural modeling of each of the anticlines helps in determining drilling trajectory.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013