Development of a Volumetric Horizontal-Well-Stimulation Model
Authors: Carpenter Chris 
Published: February 2015

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 165143, ’Development of a Volumetric Horizontal-Well-Stimulation Model,’ by Linus A. Nwoke, SPE, Shell Petroleum Development Company of Nigeria, prepared for the 2013 SPE European Formation Damage Conference and Exhibition, Noordwijk, the Netherlands, 5-7 June. The paper has not been peer reviewed.

The elliptical (conical) damage profile associated with horizontal wells is well-known, but review of industry-wide applications by different operators shows no corresponding uniform correlation between the damage profile and actual treatment volumes that have been applied. This inadequacy has often led to suboptimal post-stimulation performances. Furthermore, funds spent on stimulating horizontal wells did not yield the expected rewards; the stimulation gains are mostly short-lived because of flawed volume design and application.

Introduction

Unlike the vertical-well-damage profile, the damage profile around a horizontal wellbore is neither radial nor distributed evenly along its entire length because of formation anisotropy that creates an elliptical damage profile normal to the wellbore. The exposure time to fluids during drilling and completion operations, or the varying magnitude of fluid flow quantities across the various segments of the drainhole length during the production and injection process, will result in a truncated elliptical cone of damage along the length of the well, representing a frustum (Fig. 1) with the base of the cone nearest to the heel (near the vertical section of the wellbore).

Fluid diversion is often difficult to achieve in horizontal wells because fluids tend to take the path of least resistance, even when using mechanical diverting aids or coiled tubing. Considering the fact that large quantities of acid are required for matrix stimulation of horizontal sections, it is often desirable to assume partial damage removal, but this often results in the creation of a stimulated zone with improved permeability surrounded by a collar of damage. Notwithstanding these challenges, effective distribution of the stimulation fluid along the entire length of the well is desirable, and this is why a consideration of the nature of the damage distribution in horizontal wells is very important and key to achieving a true stimulation.

In order to address this first step in horizontal-well-stimulation fluid design, a model development was carried out to simultaneously determine the acid volume required to cover the damage area of the horizontal near-wellbore region and each of the segments as desired on the basis of operational feasibilities.

The required input parameters for the new model are the drainhole length, the number of desired treatment segments, average porosity, wellbore radius, and estimated damage radius at the heel. The output parameters from the model include the acid volume required to treat each segment of the drainhole, which decreases from the heel toward the toe in conformance with the established elliptical damage profile.