Microseismic Studies of Hydraulic Fracture Evolution at Different Pumping Rates
- Yashwanth Chitrala (U. of Oklahoma) | Carl H. Sondergeld (U. of Oklahoma) | Chandra Shekhar Rai (U. of Oklahoma)
- Document ID
- Society of Petroleum Engineers
- SPE Americas Unconventional Resources Conference, 5-7 June, Pittsburgh, Pennsylvania USA
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.9.2 Geothermal Resources, 5.8.1 Tight Gas, 2.2.2 Perforating, 3 Production and Well Operations
- 3 in the last 30 days
- 453 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 8.50|
|SPE Non-Member Price:||USD 25.00|
Our objective is to improve hydraulic fracturing through an understanding of the fracture evolution. We used real-time acoustic emission (AE) monitoring to study the samples subjected to varying pumping rates which are diametrically stressed at 650 psi. Velocity analysis indicates the compressional velocity variation is less than 2% throughout the sample, so they are treated as isotropic. Higher breakdown pressures were observed at rapid injection rates. Shear failures are commonly found at low to intermediate injection rates, whereas tensile fractures are observed at rapid pumping rates. Fracture initiation occurs at pressures lower than the breakdown pressure. However, the difference between the initiation and the breakdown pressure is less at slower injection rates. Secondary activity coinciding with the pump shutoff was commonly observed at intermediate and rapid injection rates. Higher pressurization rates were observed at rapid injection rates, but the relationship was not linear. The fracture width and length are observed to taper away from the borehole.
Hydraulic fracturing is required for the efficient exploitation of shale reservoirs. Indeed, the need for larger pumps, greater horsepower and pressure capabilities is increasing. Longer horizontal lateral lengths and greater number of fracture stages has increased the burden further. Optimization of horsepower and fracturing fluids is essential to minimize the overall fracturing costs. It, therefore, becomes important to understand the role fracturing fluid and pumping play in maximizing the reservoir contact.
The initial applications of the hydraulic fracturing include identification of the insitu stress field and extraction of the geothermal energy. Hubbert and Willis (1957) described the relations between hydraulically induced tensile fractures and insitu stresses. The interaction between the fluid and rock and the resulting change in stresses was extensively studied since the 1960's. In the literature it is assumed that the hydraulic fracture is initiated at a point when the hydraulic pressure exceeds the tensile strength of the rock. But it is observed that, by simply lowering the effective pressure to the point where the shear strength of the rock becomes less than the tensile strength, shear failure can be induced at lower pressures. Haimson's (1968) theoretical analysis of the effect of the fracturing fluid penetration, predicted lower breakdown pressures compared to those calculated by Hubbert and Willis (1957). From the initial set of laboratory hydraulic fracturing experiments conducted by Haimson (1968) and Haimson and Fairhurst (1969), tensile fractures were concluded to be the dominant. Their experiments were concentrated on porous and permeable hydrostones, where a systematic increase in the breakdown pressures was observed with pressurization rates.
|File Size||1 MB||Number of Pages||10|