A New Technology for 3-D Seismic Exploration and Development of Fractured Tight Gas Reservoirs
A 3D seismic exploration method for fractured tight gas reservoirs is developed in a study conducted for the U. S. Department of Energy. The interpretation methodology is based on three principal reservoir attributes, fracture density, clay volume, and gas content.
Seismic lineament analysis is used to map lineaments through the reservoir zone using horizon slices and time slices. We interpret that in a probabilistic sense where lineaments swarm and cluster together is where reservoir fractures are most likely to be found. Leads identified using lineament density are further screened using rock typing to identify reservoir that is more likely to fracture. A collocated cokriged clay volume map using near trace seismic amplitude (an AVO attribute) is used to identify reservoir having low clay that is interpreted to be more brittle and more prone to fracturing. Fractured reservoir and good reservoir rock do not necessarily make a drillable prospect, as reservoir fractures may provide a plumbing system to both water and gas. For prospect development a gas sensitive phase gradient AVO attribute is used to further screen the leads to insure that gas is present.
In a gas field previously plagued with poor drilling results in the San Juan Basin of New Mexico, four new wells were spotted using the methodology and recently drilled. The wells have estimated best of 12-months production indicators of 2106, 1652, 941, and 227 MCFGPD.