The pressure transient behavior of hydraulically fractured wells has been the subject of considerable study over the past few years. Several investigators have presented solutions of the fundamental equations, identified qualitative diagnostic trends and suggested interpretation techniques. This paper presents a systematic approach to the problem along with substantial observations on the potential of unique interpretations.

Pre-treatment tests are considered here as necessary. Well tests in tight formations are often of very short duration, to allow the use of established methodologies. Hence, a technique to calculate the maximum reservoir permeability from a short well test is offered.

In the case of post-treatment tests the data are treated using the convolution/deconvolution techniques and influence functions. The term "influence function" defines a relationship between pressure response and time at a constant unit surface flow rate. Although drawdown well tests have advantages over buildup tests because they are used while the well is producing, their interpretation has been hampered by varying flow rates. Conventional interpretation techniques assume either constant well flow rate or controlled variation of it. Pressure buildup tests are conducted with the well flow rate equal to zero and are, as a result, predominant.

In the case of post-treatment well tests of hydraulic fractures a lengthy buildup test and the ensuing shut-in may result in severe damage to the generated fracture. Thus buildup tests are not always desirable for post-treatment evaluation. The convolution/deconvolution techniques and influence "functions," by normalizing the pressure response to a unit flow rate, permit the use of standard techniques for the analysis of drawdown tests.

The interpretations presented here utilize new versions of pressure and pressure derivative type curves including the dimensionless fracture storage coefficient, and the dimensionless fracture conductivity. Based on observations of the sensitivity of the response to these parameters, three type curves have been developed, one for low, one for intermediate, and one for high conductivity fractures. The choice can be made on the basis of pre-treatment analysis and the fracture design. The storage and the half-length of the generated fracture can then be calculated with reasonable confidence.

You can access this article if you purchase or spend a download.