Overcoming Near Wellbore Damage Induced Flow Impairment with Improved Perforation Job Design and Execution Methods

Abstract

Optimal well productivity is achieved by establishing a clean connection to the wellbore through the near wellbore zone of drilling and completion induced permeability impairment commonly referred to as the "near wellbore damaged zone". This connection through the damaged zone is usually achieved by perforating and the effectiveness of this connection is the result of the perforating system selection, the well environment in which the perforating job is executed and what happens to the perforations after shooting and before they are used for production or injection. In the depleted oil field under study a typical completion is perforated using large diameter, high shot density tubing conveyed (TCP) guns with deep penetrating charges shot underbalanced using the classic "shoot and pull" technique. After shooting, before the guns are pulled, the well is killed. Perforation and kill related damage severely impacts these wells leading to high skin and rapid production decline. The challenge in this field is to identify the most effective perforating system and job execution method to achieve good well productivity over an extended period of time. Modeling software is utilized to predict the Productivity Ratio (PR) for different perforating systems considering gun size, charge type, shot density, reservoir characteristics and the well conditions at the time of shooting. The optimal gun system is run with gas lift on to establish underbalance conditions at the time of shooting for immediate perforation clean-up. The under balance just prior to the time of shooting is managed using a permanent down hole gauge installed in the completion string. The first well completed using this new method showed improved production of 4 times what was expected compared to similar wells in the field perforated using the shoot, pull and kill technique. Additional wells perforated using this technique show similar, higher than expected, results. This paper reviews the job design criteria, job execution requirements and an evaluation of the results for several wells in this field. Total job costs will also be evaluated. The result of this novel perforating technique is a new completion strategy for oil fields in Oman improving overall well performance. Introduction A key element of how productive a well will be is the effectiveness of the perforations. The perforation creates the path for the formation fluid to flow from reservoir to the wellbore. When the perforations are left damaged or plugged inflow will suffer over the life of the well. The quality of the perforation job design and execution is a major consideration in any completion program.