Majority of wells completed offshore Malaysia have downhole screens installed for sand and fines control. It is however observed that the PI of most of these wells drop multifold times within first few years of production. This paper illustrates the workflow with novel technique of screening such wells for stimulation to restore well production. This paper will also illustrate a few examples of actual implementation of the stimulation jobs and the excellent results from these jobs.
Hundreds of strings operated by PETRONAS in Malaysia Offshore across various fields have some form of downhole screen (standalone or as part of the gravel pack) installed to control sand and fines. Although these completions remain effective initially, but water break through results in significant PI decrease. It has been established that the predominant cause of this decline is the screen or gravel pack plugging by the fines mobilized by water which is followed in many cases by deposition of inorganic or organic scales. A workflow was developed using data from existing digital production monitoring system to identify wells showing the plugging behaviour.
The workflow used several factors such as liquid rate decline, GOR, water cut, reservoir pressure, artificial lift performance etc to shortlist a list of wells on which a detailed nodal analysis was applied to estimate gains assuming 70% skin reduction. The wells which passed the workflow and showed maximum benefit from stimulation were then grouped together such that a campaign-based execution could be done to optimize cost. Detailed customized stimulation recipe for each well was prepared and optimized well level operation program was prepared. Optimization such as using bullheading technique instead of using coil tubing in some cases was done. Stimulation treatment in 4 of the wells has been pumped successfully with excellent results and an estimated 1,000 bopd total gains. The post job oil rate is double the initial rate in many cases and even 200% more in some of the cases. Post job nodal analysis suggests up to 90% damage skin removal in these wells. Optimized operation program and campaign-based execution coupled with other cost saving measures implied that the payback time was less than 1 month. PDG data from one of the wells was used extensively to evaluate pre & post stimulation well behavior.
The high damage skin in the screen completed wells is one of the most pertinent issues which leads to significant production loss in wells offshore Malaysia. This paper details a quick and robust method to identify such wells for stimulation. The results from these stimulation jobs on candidate wells are very encouraging particularly considering the economics of the jobs. Following the success of the initial jobs, many more candidate wells have been lined up for execution in near future.