Fundamentals of Rock Mechanics

A borehole-stability model that uniquely couples the mechanical and chemical aspects of drilling-fluid/shale interactions was developed. The model allows the user to determine the optimum drilling parameters (e.g., mud weight and salt concentration) to alleviate borehole-stability-related problems with oil- or water-based drilling-fluid systems. Chemically induced stress alteration based on the thermodynamics of differences in water molar free energies of the drilling fluid and shale is combined with mechanically induced stress. These two potentials are coupled by use of the framework of poroelasticity theory to formulate the physiochemical basis of this borehole-stability model

Borehole-stability model to couple the mechanics and chemistry of drilling-fluid/shale interactions

Numerical investigation of hydraulic fracture propagation in a layered reservoir using the cohesive zone method

The impact of corrosion on the oil industry has been viewed in terms of its effect on both capital and operational expenditures (CAPEX and OPEX) and health, safety, and the environment (HSE). To fight against the high cost and the impact of corrosion within the oil industry, an overview of topical research and engineering activities is presented. This covers corrosion and metallurgy issues related to drilling, production, transportation, and refinery activities.

The impact of corrosion on oil and gas industry

Numerical simulation of gas production from hydrate deposits using a single vertical well by depressurization in the Qilian Mountain permafrost, Qinghai-Tibet Plateau, China

Considering the influence of casing, analytical solutions for stress distribution around a cased wellbore are derived, based on which a prediction model for hydraulic fracture initiation with the oriented perforation technique (OPT) is established. Taking well J2 of Z5 oilfield for an example, the predicted initiation pressure with the OPT of our model is about 4.2 MPa higher than the existing model, which neglects the influence of casing. In comparison with the results of laboratory fracturing experiments with OPT on a 400 × 400 × 400 mm3 rock sample for a cased well with the deviation of 45°, the fracture initiation pressure of our model has an error of 3.2 %, while the error of the existing model is 6.6 %; when the well azimuth angle is 0° and the perforation angle is 45°, the prediction error of the fracture initiation pressure of the existing model and our model are 3.4 and 7.7 %, respectively. The study verifies that our model is more applicable for hydraulic fracturing prediction of wells with OPT completion; while the existing model is more suitable for hydraulic fracturing with conventional perforation completion.

Hydraulic Fracture Initiation and Propagation from Wellbore with Oriented Perforation

Investigation of casing deformation during hydraulic fracturing in high geo-stress shale gas play

Modeling hydraulic fracture propagation using cohesive zone model equipped with frictional contact capability

In oil and gas drilling or geothermal well drilling, the temperature difference between the drilling fluid and formation will lead to an apparent temperature change around the borehole, which will influence the stress state around the borehole and tend to cause borehole instability in high geothermal gradient formations. The thermal effect is usually not considered as a factor in most of the conventional borehole stability models. In this research, in order to solve the borehole instability in high-temperature formations, a calculation model of the temperature field around the borehole during drilling is established. The effects of drilling fluid circulation, drilling fluid density, and mud displacement on the temperature field are analyzed. Besides these effects, the effect of temperature change on the stress around the borehole is analyzed based on thermoelasticity theory. In addition, the relationships between temperature and strength of four types of rocks are respectively established based on experimental results, and thermal expansion coefficients are also tested. On this basis, a borehole stability model is established considering thermal effects and the effect of temperature change on borehole stability is also analyzed. The results show that the fracture pressure and collapse pressure will both increase as the temperature of borehole rises, and vice versa. The fracture pressure is more sensitive to temperature. Temperature has different effects on collapse pressures due to different lithological characters; however, the variation of fracture pressure is unrelated to lithology. The research results can provide a reference for the design of drilling fluid density in high-temperature wells.

Jingen Deng

Papers

Hydraulic Fracture Initiation and Propagation from Wellbore with Oriented Perforation

Investigation of casing deformation during hydraulic fracturing in high geo-stress shale gas play

Modeling hydraulic fracture propagation using cohesive zone model equipped with frictional contact capability

Borehole Stability in High-Temperature Formations

Numerical simulation of limited-entry multi-cluster fracturing in horizontal well