Fishbone type horizontal wellbore completion: A study for pressure behavior, flow regimes, and productivity index

Abstract

Abstract This paper focuses on studying pressure behavior, flow regimes, and productivity index of oil and gas reservoirs depleted by horizontal wells with a fishbone type completion technology. The main objective is introducing an integrated approach for the favorable configuration and distribution of multilateral horizontal wells extending in porous media at arbitrary directions and arbitrary permeability trajectories. The study aims to demonstrate the advantages and disadvantages of fishbone completion in terms of transient and pseudo-steady state productivity index considering single phase flow in the porous media. It is also an attempt to propose new analytical models for the expected flow regimes and new practical solutions for estimating stabilized productivity index for different scenarios of fishbone completion. In this study, pressure distribution in the porous media is described by several analytical models considering different reservoir geometries and different multilateral horizontal wellbore configurations. These models are solved for single and dual porous media where naturally induced fractures exist. Lateral and spatial permeability are considered in these models as well as non-Darcy flow impact close to the vicinity of the wellbores in gas reservoirs. The solutions of these models are used to generate analytical models for the flow regimes that can be observed during the entire production life. Transient and stabilized productivity indices are quantified for the case of constant production rate using the observed pressure responses of fishbone type horizontal wells. The starting time of pseudo-steady state and the stabilized pseudo-steady state productivity index are used to assess the optimal configuration for fishbone completion. The observations are summarized in: 1) Pressure behavior, flow regimes, and productivity index of fishbone type horizontal wells are impacted by main wellbore and laterals distribution, however, laterals distribution in both sides of the main wellbore may not have an impact in isotropic formations. 2) Azimuth and vertical deviation angles from the main horizontal wellbore and lateral and spatial anisotropies have similar impacts because they change hypothetically the lateral length. 3) The impact of azimuth angle might be maximized by the lateral anisotropy while spatial anisotropy could maximize the impact of vertical deviation angle. 4) The conjunction points of the laterals and the main wellbore may not have a significant impact. 5) Productivity indices of fishbone type horizontal wellbores during early and late production times are less than the ones obtained by single horizontal well, however, almost identical indices are seen at intermediate production time when linear flow regime is observed. 6) The starting time of pseudo-steady state flow is controlled by the main wellbore length more than the laterals’ characteristics unless these laterals extend to reservoir boundaries. The conclusions summed up from the results of this study are: 1) Eventhough fishbone type completion could be significant solution for a lot of operation problems of long horizontal wellbore such as excessive pressure drop and wellbore instability, it is not necessary delivering optimum reservoir performance. 2) Flow regimes and flow patterns (transient or pseudo-steady state) are affected by the characteristics and distributions of the main wellbore and laterals in the porous media.