A Comprehensive Skin-Factor Model of Horizontal-Well Completion Performance

Abstract

Summary Horizontal wells or laterals are completed as openhole, slotted-liner, cased and perforated, or gravel-pack completions. We have developed a comprehensive skin-factor model to predict the performance of any of these completion types and have calibrated this model with extensive finite-element simulations of flow for a horizontal-well completion. This model can be used to predict the performance of virtually any horizontal-well completion. The new completion skin-factor model accounts for the effects of formation damage, convergent flow to perforations and slots, and flow through slots, with interaction among these effects. To account for formation damage, we extended our previous rigorous model of a damaged horizontal well to include the presence of perforations within, or extending through, the damage zone. The formation damage model is also integrated with the models of slotted-liner performance to model these completions. The model of slotted- or perforated-liner performance is made on the basis of the relationship between pressure drop and flow rate for turbulent flow in these geometries. The slotted-liner model accounts for partial plugging of the slots by grains of formation minerals or precipitates (scale). Turbulence effects are a major part of the apparent skin factor for these completion types. The model shows the recommended conditions to obtain high-productivity (i.e., low skin factor) completions in horizontal wells. In particular, the interactions among damage effects and skin effects caused by perforations or slots are shown to greatly affect horizontal-well completion performance. The models developed can be applied to design optimal completions for horizontal wells or laterals. Introduction A comprehensive model for well completions is presented in this paper, which can be used to select and design optimal completion for horizontal wells. The completion-selection process starts by determining Earth stresses, rock mechanical properties, and formation stability over the producing life of the well.1 Preventing borehole collapse and production of formation sand through the wellbore are major issues in the completion choice. Following these analyses, details of the selected completion need to be determined. An optimal completion maintains formation integrity while minimizing pressure losses through the completion hardware and the near-wellbore vicinity. Our model provides inflow performance of horizontal-well completions using skin factors. Skin is a dimensionless factor calculated to evaluate the production efficiency of a well by comparing actual conditions with theoretical or ideal conditions. The skin concept was originally introduced to account for an additional pressure drop, ?ps, caused by mechanical factors using the radial-flow solution: (Eq. 1) The skin concept has been interpreted in a wide sense to mathematically account for any deviations of the flow and pressure field in the near-well vicinity from the perfect radial flow to a wellbore radius, rw. A positive skin value indicates some damage or influences that are impairing well productivity. A negative skin value indicates enhanced productivity, typically resulting from well stimulation. The development of horizontal and multilateral wells has further complicated the skin concept because the impact of skin factors on the overall well productivity greatly depends on the well configuration and the reservoir geometry. As discussed in our previous work,2 the effects of skin on vertical- and horizontal-well production could be significantly different, even with same skin values, depending on the reservoir anisotropy and the ratio of the reservoir thickness to the drainage length perpendicular to the well. Although the effects of skin factor on well productivity are influenced by the well and reservoir geometries, skin factors are independent of those factors if radial flow occurs in the near-well vicinity. This is usually a reasonable assumption because, in most cases, the outer boundary of the reservoir is sufficiently distant from the wellbore to be insignificant on the near-wellbore scale. Thus, we can use skin factor to analyze the completion performance and identify problems in the near-wellbore vicinity.

Expandable Completion Liners: A Comparison Of Performance With Other Completion Types In The Reg and Teguentour Fields, Algeria.

“…A theoretical consideration of this is given by Furui et al (2005). They developed a comprehensive skin-factor model accounting for formation damage, convergent flow to perforations and slots, flow through slots, and interactions among these effects.…”

“…This appears as a correction to the standard equation for non-Darcy flow coefficient D in Eq. 1 by Furui et al (2005): In openhole wells, where no flow-convergence effects take place, f t =1, which commercially available software implicitly assumes is unchanged with slotted liners present. Figs.…”

“…Figs. 17 and 18 show the computed values for the various Darcy and non-Darcy completion skin terms derived using the Furui et al (2005) model for various completion scenarios. In all cases, zero slot plugging is assumed.…”

Design of flow control devices in steam-assisted gravity drainage (SAGD) completion

“…In these cases, an uneven profile is generated by difference in horizontal and/or vertical permeability distribution (Al-Khelaiwi et al 2010;Baker et al 2008;Nasr et al 2000;Yang and Butler 1992), variations in porosity (Llaguno et al 2002), water saturation heterogeneity (Baker et al 2008), variations in the distance between the wellbore(s) and fluid contacts (Al-Khelaiwi et al 2010;Baker et al 2008;Edmunds and Chhina 2001), variations in localized reservoir pressure (Al-Khelaiwi et al 2010;Tabatabaei and Ghalambor 2011), changes in capillary pressure and relative permeability along the wellbore (Wang and Leung 2015), localized skin damage or fractures (Furui et al 2005;Tam et al 2013), changes in mineralogy or wettability (Ipek et al 2008;Le Ravalec et al 2009;Pooladi-Darvish and Mattar 2002), changes in thermal properties (Bois and Mainguy 2011;Irani and Cokar 2016), changes in fluid density, viscosity, or both Larter et al 2008), and the presence or absence of in-situ emulsifiers that blend reservoir and/or introduced fluids into (Ezeuko et al 2013). With the exceptional of geospatial heterogeneity, like variations in the distance between wellbore(s) and fluid contacts, these root causes serve to change the local mobility ratio.…”

Flow Control Devices in SAGD Completion Design: Enhanced Heavy Oil/Bitumen Recovery Through Improved Thermal Efficiencies

“…In cases with long wells or high flow rates, the magnitude of wellbore pressure losses can be comparable to the drawdown in the reservoir and thus negatively impact the productivity index (PI) of the well in addition to modifying reservoir conformance (Dikken 1990;Furui et al 2005;Hill and Zhu 2008;Novy 1995;Ozkan et al 1995;. Several investigators have developed methods to calculate the pressure drop in a horizontal wellbore and determine the significance of this pressure drop to production profiles.…”