The power of TDS technique for well test interpretation: a short review

Abstract

Either pressure-transient analysis or rate-transient analysis can be interpreted by four methods: (1) conventional straight-line analysis, (2) type-curve matching procedure, (3) ACMM (automatic computer modeling matching), and (4) TDS (Tiab's direct synthesis) technique. The first three methods have serious drawbacks and are commonly misused by engineers. It does not mean they are useless since they provide good results if used properly. For example, combination of (4), (1), and (3) are strongly recommended by the authors since type-curve matching are tedious and use trial-and-error procedures. ACMM is not only the most used method, but also the most risky methodology since the non-linear regression analysis used to match the pressure test with the model output leads to multiple solutions (none uniqueness of the solution). Moreover, some engineers employ it as an inverse problem when pretending to define the model by matching the data with any model. For those who do not know the way, any transportation means is good for. This is a very wrong alternative since engineers must choose the reservoir model and the ACMM helps to find out the solution. Type-curve matching is not only risky, but tedious and it fails to provide accurate results in short tests. Conventional analysis has no way of verification and some engineers confuse the flow regimes and draw the straight line on the wrong region leading to wrong interpretations. TDS technique may be the panacea to the above-mentioned problems since it uses direct analytical solutions with information coming from characteristic points found on the pressure and pressure derivative vs. time log-log plot on which the interpreter can better define flow regimes and verify results from different sources. In this paper we demonstrate the practicability and accuracy of TDS technique with some detailed examples and results are quite well. The intention of this paper is to encourage people the use of TDS technique and provide a state-of-the-art of it. Although not mentioned, TDS technique has been used by common well test interpretation software. The power of TDS is not only based upon the accuracy and capability verification, but also the possibility of artificially created non-existing flow regimes to further estimate/verify reservoir parameters. This means the best and only accurate option for short pressure test interpretations is TDS technique. Then, an engineer is welcome to use the output results with ACMM to obtain an accurate matching.

Interpretation of pressure interference tests for wells connected by a large hydraulic fracture

“…Some applications of the TDS technique in interference testing were presented by Escobar et al (2008Escobar et al ( , 2018Escobar et al ( , 2020 for radial systems, linear and spherical systems, and naturally fractured reservoirs in radial systems, respectively. For further information on the TDS technique, refer to the works by Escobar (2015Escobar ( , 2018a and Escobar et al (2018a), Han et al (2019) introduced two models to be used with shale formations to account for the interference of two multistage hydraulically fractured wells that communicate by a large fracture. One model includes the crossflow from the reservoir matrix to the fracture, while the other one, referred to as the simple model here, does not.…”

Practical interpretation of pressure tests of hydraulically fractured vertical wells with finite-conductivity in naturally fractured oil and gas formations

“…As it is well known, both transient rate and pressure analysis are important tools for reservoir characterization and adequate interpretation of those is also important for field appraisal and decision making. As commented by Escobar et al (2018), there exists four ways of well pressure and rate data interpretation: (1) Type curve-matching, (2) Conventional straight-line, (3) Nonlinear regression analysis (computer assisted) and (4) TDS Technique. The last one can be found with detail in the books by Escobar (2015Escobar ( , 2019.…”

Pressure and Pressure Derivative Interpretation of a Well in a Completed-Perforated Multilayer Reservoir with Crossflow

“…Through simulation runs, the accuracy of the method was demonstrated and verified by synthetic examples. Detailed extension of the TDS technique for different cases has also been reported by [9], [10], and [13].…”