Stimulating Tight Gas Reservoirs: Hydro Fracturing in Offshore HPHT Gas Fields by GSPC, India

摘要

KG basin in the Eastern Offshore region of India is one of the most complex heterogeneous HPHT reservoirs in the world. Gujarat State Petroleum Corporation (GSPC) operator of the Deen Dayal West Field of KG Basin has successfully performed one of the first of its kind Hydraulic Fracturing (HF) job in world under hostile offshore environment and HPHT conditions in complex inter-bedded gas reservoir. The pressure ranged from 11000 psi to 12500 psi and the bottom hole temperature ranged from 350° F to 420° F. This paper deals with designing from scratch and executing hydraulic fracturing stimulation jobs in the said field by GSPC. It shares the results of the jobs and lessons learnt. The reservoir is sandstone with inter-bedded clay with many gas sands having close proximity to water sands. Petrophysical and reservoir data analysis indicated that the tight reservoir had to be stimulated by HF to optimise productivity. The design phase included comprehensive data gathering, log analysis, target zone selection, tailoring of HF design, finalization of specific fluid recipe for each target zone. Extensive petrophysical modelling was done to identify hydrocarbon bearing zones and underlying water bearing zones, thus the potential candidates for HF. The harsh offshore environment off the Eastern Coast of India, posed a huge logistic hurdle and the HPHT conditions led to various technological limitations in frac fluid selection, maintaining rheology at higher temperatures, proppant selection, constricting fluid damaging properties, pumping capability etc. The HF modelling efforts quantified the expected proppant distribution, propped width, individual fluid stage temperatures and the expected treatment pressure. The designs were developed to accommodate about 100 m of effectively propped fracture length (tip to tip). The stress profile and the proximity of the potential water zone around the gas zones were tested with frac design. Along with HF modelling, extensive lab evaluations of rock mechanics, geomechanics, mineralogy (XRD) as well as frac fluid stability and proppant pack conductivity at expected downhole temperature of 400° F were undertaken. Formation cores were extensively tested for core-frac fluid compatibility with regain gas permeability test, Brinell hardness test, etc. to optimise fluid composition. Rock - frac fluid - proppant interaction was studied to measure effect of frac fluid on proppant pack permeability and proppant embedment. The paper aims at providing an insight to the procedures practiced and the technology used for the stimulation of a tight gas offshore reservoir with HPHT conditions. The results and lessons learned from post frac study as shared in the paper would help the operators worldwide to plan and develop a complex offshore HPHT tight gas field.