This article captures insights from a Central/Eastern Gulf workshop on "Technologies for Developing Naturally Fractured Reservoirs" held in Shreveport in October. There, several industry speakers discussed aspects of making good wells in fractured reservoirs.

One reality with fractured reservoirs is that they can be quite susceptible to damage during drilling. Rick Stone, Signa Engineering Corp., shared how underbalanced drilling can reduce damage while providing other drilling advantages. From the reservoir perspective, there is less drilling fluid damage (filtrate invasion, solids plugging, hydration of sensitive shales/clays), less drilled cuttings damage, and less skin damage. Production and ultimate recovery are increased, and with less damage, stimulation may not be required. With regards to drilling, justifications include improved drilling rate, limit loss of circulation, mitigating differential sticking, controlling surface pressures, and increased safety. Flow drilling allows the well to flow while the well is drilled. Downhole influx and surface pressure is managed with the drilling choke. In addition to reducing damage, it enables one to evaluate formation productivity during the drilling stage itself.

One must understand the fracture system and how flow occurs through it. Conceptual models should consider geology, geomechanics, seismic, well logs, direct observation (outcrops, thin sections, cores), and physical properties. Marisela Sanchez, ITASCA Houston, Inc., shared about one approach, the Discrete Fracture Network (DFN) model. This defines a fracture distribution function, which provides the number of fractures having a given orientation and length, and belonging to a given volume of observation. It defines: (1) the probability distribution of fracture orientations, (2) the dependency on the size of the sampling domain, and (3) the fracture-length density distribution. The main scaling parameters are the fractal dimension and the power-law exponent of the fracture length distribution. Sanchez noted that fractures are deformable, responding to the in-situ stresses, pore pressure and induced stresses during the well's life. Fractures that are in shear failure (or close to shear failure) are more likely to preserve or create permeability paths. Redistribution of the stresses around the well will change the local fracture aperture and consequently will affect pressure and permeability.

In any reservoir, including fractured reservoirs, mapping of hydraulic fracturing has become an extremely useful tool. It can  provide answers about fracture orientation, fracture length and

Graphic courtesy of Pinnacle Technologies, Inc.

One has drilled, logged, modeled and mapped—the completion equipment and process brings it all together to make a good well. Rick Middaugh, Halliburton Energy Services, described the multiple completion options available—cemented pipe, uncemented pre-perforated pipe, pinpoint processes with hydrajetting, openhole packer techniques and near wellbore high energy treatments. Each has a fit—factors that determine the fit are water concerns, need for near-wellbore cleanup, removing drilling damage to the fracture system and economics.

Workshop Topics
To Look Forward To
(check calendar on
www.pttc.org for scheduling)

• Natural & Anthropogenic Subsidence Impact on Louisiana Coasts (Louisiana)

• U.S. Oil & Gas Technology Summit (U.S. Oil Expo, Mississippi)

• Coil Tubing and Slim Hole Drilling Technologies (Louisiana)

• Integrated Field Studies in Mature Areas (Louisiana)

• Basin Analysis & Petroleum Systems, Central & Eastern Gulf of Mexico (Louisiana)