Rock mechanical and failure related properties are of vital importance to various facets of the petroleum industry. Starting from drill bit selection and drilling operation to completion and stimulation design, all depend on the knowledge of rock mechanical properties. Laboratory core measurements and downhole microfrac tests are techniques that can be employed to directly measure these mechanical properties. These direct techniques, however, fail to provide continuous data through the interval of interest. Use of various geophysical logging data has made possible to obtain continuous rock mechanical data. Comparison of these log derived properties with laboratory and microfrac data have shown the need for improvement for rocks of certain type and depositional history. The improvement issue can be addressed from two perspective. First, the need for a new multiple acoustic tool to enhance shear velocity measurement in slow formations (rocks with compressional slowness greater than 90 microsec/ft) and secondly, the need for a methodology that makes use of geophysical log, core, and microfrac data to improve the rock mechanical behavior modeling. In this paper, we first discuss a methodology that improves the rock mechanical behavior modeling and then describe a new multipole acoustic tool response behavior.
With the uncertainty in oil price it has become important to optimize drilling and stimulation treatments to maintain profitability. One of the critical aspects of drilling and hydraulic fracture treatment design is the prediction of rock failure and propagation geometry (Veatch 1982, Ahmed 1988). There are various fracture geometry prediction (Clifton and Abou-Sayed 1981, Veatch 1982, Lam er al: 1986, Economides and Nolte 1987) and drilling design (Affleck and Zamora 1987, Damron et al. 1988) models available to the industry. Proper use of these models require the knowledge of continuous in-situ stress and mechanical properties of the producing formation and bounding non-producing layers (Ahmed 1988). The microfrac technique is considered by far to be the best method to directly measure in-situ stress (Warpinski et al. 1980, Voegele et al. 1981). The technique, however, has certain limitations. At times it may be impractical to breakdown and measure in-situ stress in bounding non producing layers. In cased hole this technique is dependent upon good bond between the cement and the casing, and the formation as well. Microfrac measured in-situ stress in a well without adequate cement bond may be representative of an adjacent layer which was in hydraulic communication with the perforated interval. Use of the technique over intervals of varying stresses can also lead to inconclusive results. When injected volumes are increased to the point where the fracture migrates into adjacent layers of varying stress, the computed in-situ stress value may no longer be representative of the originally perforated layer. Alternate techniques include core testing and well logging. Core testing can provide stress measurements via stress-strain relaxation methods (Teufel 1983, Thiercelin et al. 1986). Under ideal conditions of core recovery and gauge resolution, the calculated values can be within an acceptable range (Economides and Nolte 1987).
