Pre and Post Gravel Pack Pressure Transient Testing of Layered Reservoir Wells (original) (raw)

Proceedings of SPE Production Operations Symposium, 1997

Abstract

Permeability and skin factor can be misestimated from well testing data taken after completing wells in layered reservoirs. Results presented in this paper are based on field data and numerical simulation work on two wells in an offshore Louisiana field. Testing results taken after completing the first well in the field with a gravel pack, gave considerably lower than expected permeability results that could have jeopardized the future development of the field. Well performance analysis based on pre-gravel pack flow, as well as investigation of existing well log data, indicated the possibility of a layer of higher permeability within the tested interval. In consideration of this analysis, a decision was made to proceed with the drilling of a second well in the field and perform a pre-gravel pack test to obtain original reservoir data. Then, the completion design for the second well and the treatment strategy for the first well would be based on the proposed pre-gravel pack test results of the second well. The pre-completion impulse testing of the second well, drilled to the same reservoir, gave a higher calculated permeability than the first well, confirming our expectation. A new completion design was proposed and implemented on the second well. Post-completion transient testing indicated that the second well completion maintained communication with the higher permeability layer allowing the evaluation of the well completion skin. The new reservoir permeability then used in reservoir simulation resulted in a more reliable field production performance prediction and evaluation. Well log data, well test data, completion design, and reservoir simulation results are presented in this paper. Introduction Poorly consolidated sandstone intervals are usually gravel packed to control sand movement into the wellbore when the well is on production. As it is known to negatively impact formation productivity at the wellbore damage should be minimized during both drilling and completion operations. This damage can usually be estimated from well test interpretation and is referred to as a skin value. However, in a multi-permeability layered reservoir, the amount of formation damage in each layer will be proportional to it's permeability. During well testing, this may result in significantly lowering the contribution of the highly damaged zone, and hence cause a misestimation of the effective permeability and skin. A basic description of transient flow models in homogenous, and layered reservoirs is presented in the next paragraphs. Description of transient flow regimes in different reservoir models has been presented by several authors. The system of equations governing transient flow of fluid in homogeneous porous medium is; (1) (2) (3) (4) The semilog analysis solution to this problem using the Boltzmann transform approach is; (5) P. 231^

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