Unconventional Reservoir Shale Gas
Geophysics, Banaras Hindu University, Varanasi, India.
Shale gas is natural gas from shale formations which acts as both the source and the reservoir for the natural gas. Each Shale gas reservoir has unique characteristics. Research work focus at bridging the gap between invariant characteristics at nano scale of sedimentary rocks and their macroscopic properties. 3D seismic is becoming successful because of the ability to identify fracutre and fault trends. Surface geochem cannot identify in the subsurface where the frac or fault systems will be intersected by the drill bit. This is why 3D is now being used aggressively and successfully. Unconventional reservoirs require some form of stimulation to obtain commercial production. Shale gas reservoirs require fracture stimulation to unlock gas from extremely low-permeability formations. As fracture stimulation is an important aspect of well completions, production companies need to know basic information about fractures such as whether they will open, direction of fracture propagation, dimensions and type of fracture, and whether they will stay in zone. The hydraulic fracturing is used to increase or restore the rate of fluid flow within the shale reservoir and horizontal drilling creates maximum borehole surface area in contact with the shale. In addition to water and proppant ,nano enhanced proppant(OxBall and OxFrac light, high-strength ceramic proppants) other additives are essential to successful fracture stimulation. Geophysicist derives a host of geomechanical properties from migrated common depth point gathers, including Young's Modulus, Poisson's Ratio, and shear modulus, by first inverting the data for P- and S-wave velocities and density. With this information, fracture dimensions can be predicted and wells drilled in the most brittle rock.Linear Slip Theory for geomechanical properties is used to calculate stress values. Ultrasonic Measurements of Anisotropy of Shales: Laboratory measurements of ultrasonic velocities have confirmed that compressional waves travel faster in the direction of applied stress. The reason may be that all rocks contain some distribution of microcracks. A clear understanding of the geomechanical properties and their distribution explains the reservoir heterogeneity and thus the variation in economic ultimate recovery between wells. Generally, the stress state is anisotropic leading to the estimation of both the minimum and maximum horizontal stress.
AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012