A Complete Hydraulics Model for Horizontal Wells

Abstract

SPE Members Abstract A horizontal well usually yields a high rate through its long perforation interval, resulting in a large frictional pressure drop that is believed to reduce the well productivity. Unlike conventional horizontal well methods which consider the horizontal section only, the proposed model also includes the vertical section of the well and the surface facility from the well head to the GOSP. The hydraulics model was validated stage-by-stage by various known solutions, and then applied to a high rate well. It was found that the effect of frictional pressure drop on oil rate was not as pronounced as suggested by analytical methods, or some numerical simulation studies. In summary, the pressure drop in the vertical section of the horizontal well plays an especially important role in deciding how much fluid can be produced. Therefore, it is recommended to be an integral part of horizontal well models. Introduction In models which consider the horizontal section only, frictional pressure drop was shown to reduce the productivity of horizontal wells. Dikken presented an analytical horizontal well model that combined the fluid flow in the horizontal section of a well and the reservoir flow. He concluded that the flow inside horizontal wells is either transition or turbulent in most practical situations. Furthermore, for single phase turbulent flows, he found that appreciable reduction in drawdown occurred at positions farther away from the start of the section. In a water coning example, he demonstrated that little additional production results from extending a 300 m long well with a diameter of 11.4 cm. Novy generalized Dikken's model so that it can be applied to the recovery of gas. In the process, he found that the friction factor correlation used by Dikken gives friction factors that are too high for rough tubes. Novy performed extensive sensitivity studies and he concluded that if the ratio of well-bore pressure drop to drawdown at the producing end exceeds 10%, friction is apt to reduce productivity by 10% or more. In a simulation study where the frictional pressure drop was included in the horizontal well model, Seines et al. found that by varying the effective roughness of the well, thereby changing the pressure drop, they obtained a 10% difference in cumulative production after 1 year. The well was producing at a fixed flowing bottomhole pressure (FBHP). This paper presents the work in which a complete hydraulics model for horizontal wells was developed and validated. The model was then applied to a high flowrate case. Calculated results were compared with analytical predictions. Investigation of the discrepancy in results provided some insights about the modeling of horizontal wells. P. 407

Modelling flow for finite conductivity in long horizontal oil wells

“…Studies have shown that Dikken (1990) is unrealistic based on assumption of infinite flow conductivity in the horizontal section of the well that was applied in his model derivation. Though several accessible mathematical models (Landman, 1994;Ozkan et al, 1993;Penmatcha et al, 1997;Siu and Subramanian, 1995;Yildiz and Ozkan, 1998) that considered finite flow conductivity in derivation for predicting the productivity of horizontal wells have been coded and generated into commercial software in the oil industry, but rarely attractive due to the common nature of either simplicity if it too analytical or rigorous and time consuming in computation if it too numerical. The mathematical models used for predicting horizontal drain hole productivity that are available fall into three categories: (1) simple analytical solutions derived in late 1980s and early 1990s based on the assumption of frictionless drain holes, Generally, these models are embraced because they are simple and very easy to use.…”

Development and investigation of integrated reservoir-wellbore flow model

“…In addition to theoretical models, some researchers have simulated wellbore flow using numerical techniques to avoid simplifying assumptions (Ouyang and Huang, 2005;Yuan et al 1998;Su and Lee, 1995;Siu et al 1995;Seines et al 1993;Folefac et al 1991). Guo et al (2006) developed a numerical model to study the deliverability of multilateral wells.…”