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

Abstract

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.

Keywords

• Vertical anisotropy
• Limited entry
• Partial penetration
• Partial completion
• Formation testing
• Short tests