New Method To Estimate Damaged Formation Permeability With Well Testing

New Method To Estimate Damaged Formation Permeability With Well Testing Liangwen Zhang; Liangwen Zhang U. of Waterloo Search for other works by this author on: This Site Google Scholar Maurice B. Dusseault; Maurice B. Dusseault U. of Waterloo Search for other works by this author on: This Site Google Scholar Baoci Xu Baoci Xu U. of Waterloo Search for other works by this author on: This Site Google Scholar Paper presented at the SPE International Symposium and Exhibition on Formation Damage Control, Lafayette, Louisiana, USA, February 2006. Paper Number: SPE-98200-MS https://doi.org/10.2118/98200-MS Published: February 15 2006 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Zhang, Liangwen, Dusseault, Maurice B., and Baoci Xu. "New Method To Estimate Damaged Formation Permeability With Well Testing." Paper presented at the SPE International Symposium and Exhibition on Formation Damage Control, Lafayette, Louisiana, USA, February 2006. doi: https://doi.org/10.2118/98200-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE International Conference and Exhibition on Formation Damage Control Search Advanced Search AbstractMost composite solutions used in modern well test interpretation use the "step-permeability" model where the altered formations are divided into two or more concentric zones, each with constant permeability. Depending on the causes of alteration or variation, this model can deviate significantly from the real condition. A formation can be altered because of stress redistribution, drilling damage, solids co-production, mineral precipitates, and drilling mud invasion, each factor more likely to generate spatially-varying permeabilities rather than constant k zones. Experimental data confirm that a continuous permeability model is more realistic than the step permeability model.A new semi-analytical solution with smooth radius-dependent permeability has been developed to analyze well test results from such altered formations. The altered formation is approximated as a concentric two-zone composite model: an exterior intact zone that retains the original unaltered permeability, and an interior zone where the permeability values have been altered and change as a function of radius. The permeability in this near-well zone can change continuously to the original permeability or to a different value at the boundary with the exterior zone, where there is a step-change in permeability. The choice of an increase or decrease of permeability with radius within the altered zone depends on the nature of the actual alteration. The permeability can also be simulated as a step-wise function if appropriate parameters are used; in such situations, the model collapses to conventional step-wise composite models. Other parameters such as formation porosity and compressibility of each zone can also be different, but they are assumed constant for this derivation. The new solution is derived in Laplace space, and numerical Laplace inversion is used.IntroductionWell test interpretation is widely used in estimating formation parameters such as permeability. Early well test solutions by Muskat[1] assumed a fully penetrating well in a homogeneous, isotropic, and infinite formation; the condition of constant permeability, however, has been recognized as inadequate in many field applications (Sabet[2], Freeze and Cherry[3]). Non-uniformity of permeability arises mainly from two factors. The first is natural heterogeneities inherited from existing geological structures in the formation being tested; Streltsova[4] has a fairly detailed discussion on this category. The second factor is formation alterations caused by engineering development processes. In this paper, we focus on the latter.Near-wellbore permeability can be altered as the result of physical processes such as sand production, drilling-induced stress redistribution, drilling damage, fine-grained material migration, carbonate or asphaltene precipitation, drilling mud invasion, thermal injection effects such as formation shear dilation, or some combination of these. Different methods have been proposed to assess permeability alteration effects on well productivity and well test interpretation. The "skin term" model first presented by Hawkins[5], and used extensively by reservoir engineers (Robert[6]), is probably the earliest attempt to quantify permeability alteration. The skin term was introduced as a small, zero-thickness flow impedance factor, which is positive or negative depending on whether well productivity is decreased (+ve) or increased (-ve). The skin term is obtained by assuming that steady-state pressure conditions exist in the skin, which in reality, with a significantly thick altered zone, may only be true at late stages of well tests, when the unaltered zone dominates production. As noted by Abbaszadeh[7] et al, depending on the size of the altered zone, times to steady-state can be very different.A weakness of skin term interpretation is that it gives little useful information to determine the nature of the permeability alteration. Hence, composite models have been proposed, such as those of Olarewaju[8] et al., Butler[9], and Novakowski[10,11]. These models are based on an axisymmetric, two-annulus altered formation around the wellbore; permeability is assumed constant in each zone, with an abrupt change at the interface between zones. We refer to these as "step-permeability" models because permeability varies as a step-wise function with radius. Keywords: flow in porous media, drillstem/well testing, composite model, boundary condition, pressure transient analysis, Upstream Oil & Gas, unaltered zone, Formation Permeability, pressure transient testing, compressibility Subjects: Reservoir Fluid Dynamics, Formation Evaluation & Management, Flow in porous media, Pressure transient analysis, Drillstem/well testing This content is only available via PDF. 2006. Society of Petroleum Engineers You can access this article if you purchase or spend a download.

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