Abbas Ali Daneshy

A Study of Inclined Hydraulic Fractures

The results of a theoretical and experimental investigation of inclined hydraulic fractures, indicate that such fractures do not generally initiate perpendicular to the maximum tensile stress induced on the borehole wall. Unlike axial or normal hydraulic fractures, a degree of shear failure seems to be associated with the initiation and extension of almost all inclined hydraulic fractures. These fractures often intersect the borehole along 2 diametrically opposite axial lines, thus giving it the appearance of an axial fracture. Inclined hydraulic fractures generally change their orientation as they extend away from the wellbore until they become perpendicular to the least compressive in situ principal stress. Therefore, the borehole trace of such fractures cannot be used for their positive identification.

Numerical Solution of Sand Transport in Hydraulic Fracturing

A numerical solution is developed for the deposition of a propping agent inside a hydraulic fracture. Such parameters as fluid leak-off into the formation, increase in sand concentration caused by leak-off, non-Newtonian fracturing fluids, hindered settling velocity, and an up-to-date geometry are taken into consideration. Three examples investigate the proppant deposition for low-, medium-, and high-viscosity fracturing fluids.

On the Design of Vertical Hydraulic Fractures

Some of the assumptions involved in designing vertical hydraulic fractures should be critically examined as to their validity. This is done on the basis of a new width equation and a numerical design procedure. It is found that some of the assumptions related to the fluid mechanics of the problem greatly affect the computed results and therefore deserve special attention. (18 refs.)

Hydraulic Fracture Propagation in the Presence of Planes of Weakness

A study is made of hydraulic fracturing of formations containing natural flaws. The 3 factors of importance are shown to be the strength of the weakness plane, its orientation with respect to the least compressive principal stress, and the difference between the principal stress magnitudes. Material flaws with dimensions that are small compared with the induced hydraulic fracture are shown to be unable to change the overall orientation of the hydraulic fracture. The induced fracture can encircle such material defects and override their possible effect. Even if it does not, the influence of these flaws is local and insignificant on the results of the fracturing treatment. Large material flaws are shown unable to drastically change fracture orientation. The analytical results presented in the paper are based on the principle of least resistance. The study does not include severely fractured, highly permeable formations.

In-Situ Stress Measurements During Drilling

This paper describes the results of six microfracturing experiments in a gas well in south Texas. The experiments were conducted in open hole and during the drilling operations. Microfracturing consisted of pumping very small volumes of drilling mud (tens of gallons) at very low rates (3 to 30 gal/min (189 to 1892 x 10 /sup -6/ M/sup 3//s)). Three of these microfractures extended below the bottom of the open hole and were cored out. Created fracture orientation was obtained from the fractures observed in the oriented core. Several instantaneous shut-in pressures recorded in each zone showed variations of about 200 to 300 psi (1.4 to 2.1 MPa). This magnitude change is attributable to heterogeneity of the rock. Measured values of instantaneous shut-in pressure (ISIP) did not show any trend with lithology (shale or sandstone), mechanical properties, or tensile strength.

Effect of Treatment Parameters on the Geometry of a Hydraulic Fracture

The parameters influencing the geometry of a hydraulic fracture are divided into 3 categores: (1) those upon which there is no control, such as Youngs modulus and Poissons ratio of the formation, far-field stress and the reservoir pressure; (2) those which are easily controlled such as treatment-fluid viscosity and time; and (3) those which are partially changeable, like fluid leak-off and injection rate. A study is made of the effects of each individual parameter on the geometry of a hydraulic fracture. Based on the findings reported, it is concluded that at the present time, the treatment-fluid viscosity appers to be the most promising factor for influencing the geometry. Increasing the viscosity has 2 effects. Directly, it increases the width of the generated fracture, thus yielding better conditions for the transportation of the propping agents. Indirectly, it reduces the volume of fluid lost as leak-off. Another important conclusion is that the computed fracture geometries are, to a large degree, influenced by the assumed value of the fracture height. A reasonable geometry can be obtained only if one assumes a reasonable value for the fracture height.