What are the most effective ways to perforate a wellbore during drill stem testing?

1 Tubing-conveyed perforating

Tubing-conveyed perforating (TCP) is a technique that involves running a perforating gun attached to the bottom of the tubing string and setting it off with a firing head or a pressure-activated switch. TCP allows for deep and accurate penetration of the formation, as well as immediate flowback of the fluids through the tubing. TCP is suitable for DST in high-pressure, high-temperature, or deviated wells, where wireline perforating may not be feasible or safe. TCP also enables selective perforating of multiple zones with different guns and packers.

2 Wireline perforating

Wireline perforating is a technique that involves lowering a perforating gun into the wellbore on an electric wireline and detonating it with an electric signal from the surface. Wireline perforating allows for precise control and measurement of the perforating depth and orientation, as well as easy retrieval of the gun and debris. Wireline perforating is suitable for DST in vertical or slightly deviated wells, where the wellbore is stable and clear of obstructions. Wireline perforating also allows for multiple runs of different guns and tools, such as pressure gauges or samplers.

3 Coiled tubing perforating

Coiled tubing perforating is a technique that involves pumping a perforating gun through a coiled tubing and firing it with a hydraulic or electric trigger. Coiled tubing perforating allows for rapid and continuous deployment and recovery of the gun, as well as circulation of fluids or chemicals during or after the perforation. Coiled tubing perforating is suitable for DST in wells with complex geometry, such as horizontal or multilateral wells, where conventional perforating methods may not reach or cover the target zones. Coiled tubing perforating also allows for real-time monitoring and adjustment of the perforating parameters and performance.

4 Underbalanced perforating

Underbalanced perforating is a technique that involves perforating the wellbore when the reservoir pressure is higher than the wellbore pressure, creating a flow of fluids from the formation into the wellbore. Underbalanced perforating allows for enhanced productivity and reduced damage of the reservoir, as well as improved cleanup and evaluation of the fluids. Underbalanced perforating can be achieved by using any of the above methods, but with special precautions and equipment to maintain the pressure differential and to handle the influx of fluids. Underbalanced perforating is suitable for DST in tight, low-permeability, or damaged reservoirs, where conventional perforating methods may not create enough flow or recovery.

5 Selecting the best perforating method

When selecting the best perforating method for DST, a number of factors must be taken into account, such as the reservoir characteristics, the wellbore conditions, the testing objectives, and the operational constraints. You should consider the depth and extent of the perforation, the orientation and alignment of the perforation, the safety and efficiency of the perforation, as well as the cost and availability of the perforation. By carefully evaluating each method based on these factors, you can select an effective way to perforate a wellbore during DST and achieve optimal results.