Impact Of Completion On Wellbore Skin Effect
- Mohammed H. A. Alshawaf (Saudi Aramco) | Alain Gringarten (Imperial College)
- Document ID
- Society of Petroleum Engineers
- EAGE Annual Conference & Exhibition incorporating SPE Europec, 10-13 June, London, UK
- Publication Date
- Document Type
- Conference Paper
- Society of Petroleum Engineers
- 1.6 Drilling Operations, 5.1.1 Exploration, Development, Structural Geology, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.2.1 Phase Behavior and PVT Measurements, 2.2.2 Perforating, 2.4.6 Frac and Pack, 1.8 Formation Damage, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.4.3 Sand/Solids Control, 2.4.5 Gravel pack design & evaluation, 1.11 Drilling Fluids and Materials, 5.3.2 Multiphase Flow, 3.2.5 Produced Sand / Solids Management and Control, 4.2 Pipelines, Flowlines and Risers, 5.6.4 Drillstem/Well Testing
- Perforations, Frac-pack, skin effect, Completion, Gravel pack
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Wellbore completions are a key well component and could have a positive or a negative impact on productivity, thus designing a suitable completion and implementing it properly must be a priority for production engineers. Consequently, well productivity indices related to specific completion designs have received much attention in the literature, with analytical and numerical models used for simulating various completion properties. The completion impact on wellbore skin effect, however, is seldom documented.
This paper looks at the effect of completion and reservoir characteristics on skin factors, and focuses on perforated, gravel-packed and frac-packed wells. For this study, a commercial black oil simulator was used to simulate different reservoir conditions and completion strategies, and the resulting skin effects were estimated by well test analysis of the corresponding synthetic pressure and rate data.
Results show that decreasing perforation density and tunnel length leads to high skin values due to wellbore flow restrictions. Moreover, it shows how a damaged gravel-pack completion coupled with a highly permeable formation results in high skin values that range between 1 and 100. Finally, in frac-pack completions, it is important to find the right balance between formation permeability and proppant permeability in the fracture as well as the permeability contrast between the proppant and the gravel as this dictates how a frac-pack will perform. Thus, depending on permeability of proppant and gravel-pack, skin values for frac-pack completions range between -2.5 to 15
In the early days of the oil industry, wells were completed open-hole or barefoot, i.e. the only restriction to oil or gas flow into the well was due to drilling induced damage, mainly caused by the drilling mud. More difficult reservoir conditions such as increased depth, tight formations or unconsolidated sands, for example, have forced operators to utilize different completion schemes in order to mitigate possible associated risks. Examples of such risks include severe pressure drop around the wellbore that hinders well productivity, and uncontrollable sand production that damages bottom-hole and surface equipment. Over time, new completion techniques were developed, such as perforations, gravel-packing wells and frac-packing.
Associated with completions is a wellbore skin effect, which creates a pressure drop around the wellbore. The concept was introduced by van Everdingen (1953) and Hurst (1953), after they observed a greater pressure drop near the wellbore in buildup analysis than had been expected. While the skin concept is routinely used in the oil and gas literature to quantify the well condition, there is little information on wellbore skin values associated with specific completion designs. This paper intends to fill this gap by evaluating completion induced skin effects, as a function of reservoir and fluid properties as well as completion characteristics. The focus is on perforated, gravel-packed and frac-packed wells.
|File Size||1 MB||Number of Pages||13|