Transient Pressure Analysis for a Vertical Gas Well Intersected by a Finite-Conductivity Fracture Walter Nunez; Walter Nunez Ecopetrol Search for other works by this author on: This Site Google Scholar Djebbar Tiab; Djebbar Tiab University of Oklahoma Search for other works by this author on: This Site Google Scholar Freddy H. Escobar Freddy H. Escobar Universidad Surcolombiana Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Production and Operations Symposium, Oklahoma City, Oklahoma, March 2003. Paper Number: SPE-80915-MS https://doi.org/10.2118/80915-MS Published: March 23 2003 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Nunez, Walter, Tiab, Djebbar, and Freddy H. Escobar. "Transient Pressure Analysis for a Vertical Gas Well Intersected by a Finite-Conductivity Fracture." Paper presented at the SPE Production and Operations Symposium, Oklahoma City, Oklahoma, March 2003. doi: https://doi.org/10.2118/80915-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Oklahoma City Oil and Gas Symposium / Production and Operations Symposium Search Advanced Search AbstractPressure-transient analysis for gas wells has a great importance in the oil and gas Industry. Transient pressure responses of unfractured and hydraulically fractured gas wells may be affected by non-Darcy flow near the wellbore, such important effect needs to be taken into account when estimating reservoir and well parameters. An additional problem encountered in gas wells test analysis is the presence of the rate-dependent skin, which requires a search for another parameter (non-Darcy flow coefficient).Several tests are performed in order to measure the deliverability of gas wells and to describe reservoir performance. Such specific tests as flow after flow, isochronal and modified isochronal were initially designed to obtain the absolute open flow potential of a well, however, the use of these tests has been extended to obtain additional information from the reservoir. Drawdown tests are focused in obtaining such data as wellbore storage, reservoir transmissivity, skin factor, flow efficiency and system geometry. Buildup tests lead us to the average pressure of the reservoir, however, proper analysis of buildup test provides values of permeability, wellbore storage and apparent skin factor. Buildup and drawdown tests are currently analyzed using type-curve matching procedures, which involves trial and error and conventional techniques.Pseudopressure concept, which was used in this study, has shown to provide sufficient engineering accuracy in dealing with gas well test data. This study utilizes characteristic points, intersection and lines found on the pseudopressure and pseudopressure derivative plot to obtain fracture length, fracture conductivity, skin factor and reservoir permeability.It was found that changing the non-Darcy factor, D, the shape of the pseudo-pressure curve varies from the original gas curve shape at D=0, which implies that an additional skin effect is added at high rates. On the other hand, the pseudo-pressure derivative curve remains on its original shape, then, in spite of increasing non-Darcy effect factor, D, the pseudo-pressure derivative curve is not affected by this additional skin effect added to the system because of the non-Darcy flow effect. The interpretation technique was successfully tested with simulated and field examples.IntroductionIn 1999, Tiab et al.1 extended the Tiab's Direct Synthesis Technique for interpretation of the behavior of the pressure and pressure derivative data of an oil well intersected by a finite-conductivity hydraulic fracture. Now, this study extends the Tiab's Direct Synthesis Technique usage to vertical gas wells, which also closely follows the procedure outlined by Tiab et al.1.During a test on a hydraulically fractured well, initially, fracture-linear flow occurs into the fracture, which is characterized by a slope of 0.5 in a log-log plot. During this fluid period, most of the fluid entering the wellbore comes from fluid expansion in the fracture, the occurrence of this flow period is too short and normally is never seen. Bilinear flow2, which is characterized by a slope of 0.25 on the log-log plot, takes place in finite-conductivity fractures as fluid in the surrounding formation flows linearly into the fracture, most of the fluid entering the wellbore during this flow period comes from the formation. Fractures are considered to have finite-conductivity when Dimensionless Fracture Conductivity2, CfD <100.Fracture conductivity has been described as having values varying typically from 1 to 500. A low value of conductivity indicates low fracture permeability or long fracture lengths, or possibly both. On the other hand, a high value of conductivity implies high fracture permeability, small fracture length, or both. Formation-Linear flow occurs only in high conductivity fractures (CfD>100), this flow is also identified by a slope of 0.5, once the linear flow in the formation -or the bilinear flow- vanishes, the pseudo-radial flow takes place.In order to define the system, consider a vertically fractured gas well producing from a horizontal, homogeneous and isotropic formation. The permeability is constant, the thickness is uniform, and the fracture is the same length on both sides of the well. Keywords: drillstem/well testing, half-fracture length, reservoir, flow regime, drillstem testing, upstream oil & gas, tiab, flow rate, derivative curve, bilinear flow line Subjects: Formation Evaluation & Management, Drillstem/well testing This content is only available via PDF. 2003. Society of Petroleum Engineers You can access this article if you purchase or spend a download.