Schlumberger

Case Study: PURE System Eliminates Need for Acid Stimulation in Well Completion, Saves 24 Hours’ Rig Time

Clean perforating method increased productivity and eliminated acid wash for operator in Middle East

Challenge: Complete a well without the use of a high-pressure coiled tubing (HPCT) acid wash.

Solution: Use PURE clean perforations system to create dynamic underbalance and maximize cleanup without acid stimulation.

Result: Efficiently completed well without use of an acid wash, saving 24 h of rig time and USD 150,000.

Maximizing production and injectivity without acid stimulation

An operator was preparing to complete one of its gas wells that historically used a two-stage acid fracture stimulation on both the lower zone and the upper zone in a low-permeability carbonate gas reservoir. As part of the normal acid stimulation process, an HPCT acid wash is performed before the acid stimulation to establish injectivity. In the past, the operator employed underbalanced perforating to eliminate the need for the HPCT acid wash but was not achieving significant cleanup. In other instances, large static underbalance conditions caused the perforating guns to be lifted in the wellbore, and subsequently the guns became stuck.

In this well, the lower zone’s proximity to the gas-water contact presented an additional problem, and an acid stimulation could not be performed on the zone. Based on past experience, the lower zone was expected not to flow without an acid stimulation.

Solution found in dynamic underbalance of PURE system

After consulting with Schlumberger, the customer chose to use the PURE system to maximize perforation cleanup in the well’s completion. In this method, perforating guns can be fired with the wellbore in static pressure balance with the reservoir pressure. The PURE system ensures control over the degree of under- or overbalance to promote cleanup of the perforation tunnels immediately after the guns fire.

Schlumberger used the well and reservoir characteristics to design a gun system to produce dynamic underbalance conditions to maximize perforation cleanup. Analysis suggested that the perforating skin in the well could be reduced from 7 to a value close to zero. The customer chose to perforate both the lower and upper zones with a gun configuration using the PURE system.

Eliminating acid wash saves over 24 h of rig time

Initially, it was not known whether the zones would flow without an acid stimulation. Following perforation, however, the lower zone produced 8 Mcf at 1,900 psi, which would provide 20 Mcf at full production. The lower zone was isolated following the first perforation run, and the upper zone was then perforated and injected at an increased rate of 5 bbl/min at 3,000 psi and flowed back at a final rate of 58 Mcf/d.

This application represented the first use of the PURE system in the Middle East. The production achieved in this well exceeded the customer’s expectations and was not considered achievable without an acid stimulation. The elimination of the HPCT acid wash on the upper zone saved over 24 h of rig time and USD 150,000.


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