Performance of Horizontal Wells Completed with Slotted Liners and Perforations

Abstract

This paper presents a comprehensive study on the productivity and flow efficiency of horizontal wells completed with slotted-liners or perforations. The study is based on a semi-analytical model that couples the flow equations in the reservoir and wellbore. The reservoir model takes into account the 3D convergence of flow around perforations and slots. The wellbore flow model considers the pressure losses inside the horizontal well and the effect of axial influx at the perforations and slots. A new, experimental apparent friction factor correlation is used for horizontal wellbore flow computations with perforations and slots. The model is capable of incorporating the effects of selective completion and non-uniform skin distribution. The results of this study indicate that software based on detailed semi-analytical models can provide a powerful tool to design, predict, and optimize horizontal well completions. It is also shown that horizontal wells deserve genuine guidelines to optimize their completions. For example, horizontal wells are shown to require significantly lower slot and perforation densities to accomplish optimum PI compare to vertical wells. Similarly, in horizontal wells, the effect of slot or perforation phasing becomes more important as the anisotropy of the formation increases. Introduction Horizontal wells are one of the most important strategic tools in petroleum exploitation.1 As a result of the advances in drilling and completion technologies in the last two decades, the efficiency and economy of horizontal wells have significantly increased. Today, horizontal well technology is applied more often and in many different types of formations. The state of the art applications of horizontal well technology require better completion designs to optimize production rates, long-term economics, and ultimate producible reserves. Horizontal well completions can be categorized as natural completion, sand-control completion, and stimulation completion. Natural completion includes open-hole, slotted-linear, and cased and perforated completions. Sand-screens, prepacked screens, and gravel packing are the completions used for sand-control. Stimulation completion includes completion with hydraulic fracturing and fracturing with gravel packing (fracpack or stimpack). All of these completion methods have been used in practice under different reservoir conditions.2,3,4 In a horizontal well, depending upon the completion method, fluid may enter the wellbore at various locations and at various rates along the well length. Fig. 1 illustrates the interplay between the pressure and flux distribution along the wellbore through the completion openings. The complex interaction between the wellbore hydraulics and reservoir flow performance depends strongly on the distribution of influx along the well surface and it determines the overall productivity of the well. Therefore, the optimization of well completion to improve the performance of horizontal wells is a complex but very practical and important problem. The complexities of the numerical simulation of horizontal well completions make analytical models extremely attractive. However, the inherent difficulties of the analytical solutions caused by the complex flow geometries, excessive number of perforations or slots, and non-uniform distribution of flux along the horizontal well calls for the challenging task of developing efficient computational algorithms.

Pressure Transient Solutions for Vertically Slotted-Partially Penetrated Vertical Wells in Porous Media

“…They compared their solutions with the middle point, equivalent-pressure point, and pressure-averaging solutions given in the petroleum literature. In addition to the recent Biryukov and Kuchuk (2012) paper, a few other papers were also published on selectively perforated and/or completed wells, i.e., wells with multiple production slots (ring slots along the wellbore), specially Spivak and Horne (1983), Larsen (1993), Yildiz and Cinar (1998), Tang et al (2000), Yildiz (2002aYildiz ( , b, 2004Yildiz ( , 2006a. The Spivak and Horne (1983) vertically slotted-liner solution, which is obtained from the uniform-flux solution, is somewhat similar to the solutions given in this paper.…”

Perforating

“…Figure 6-43 shows that productivity changes with the change of perforation density under the condition of a perforation penetration depth approximate to zero. When perforation density increases to a certain value, the increase of perforation density may not lead to an obvious increase of horizontal well productivity [8]. When perforation density increases to a higher value, the perforated well productivity will reach the open hole productivity.…”

“…It should especially be noted that under a relatively low perforation density, the productivity ratio of a horizontal well is much higher than that of a vertical well; that is, the perforated completion of a horizontal well can still obtain the desired productivity ratio under a lower perforation density. Figure 6-44 shows the effects of perforation penetration depth and perforation density on horizontal well productivity ratio [8]. The productivity ratio increases with the increase of perforation penetration depth.…”

“…3. Phase angle Figure 6-45 shows the effect of phase angle on horizontal well productivity ratio under the condition of serious anisotropy (K v /K h ¼ 0.01) [8]. It indicates that the effect of phase angle on productivity ratio is obvious and the phase angle of 180 is most favorable, while the phase angles of 90 and 45 have a lower productivity ratio.…”

“…4. Degree of heterogeneity Figure 6-46 shows the effect of degree of heterogeneity (K v /K n ) on horizontal well productivity ratio [8]. It indicates that under the condition of great perforation penetration depth, the more serious the heterogeneity, the higher the productivity ratio; however, under the condition of small perforation penetration depth, the more serious the heterogeneity, the lower the productivity ratio.…”