Analyses and Applications of Pressure, Flow Rate, and Temperature Measurements During a Perforating Run

Abstract

Analyses and Applications of Pressure, Flow Rate, and Temperature Pressure, Flow Rate, and Temperature Measurements During a Perforating Run Summary. Perforating technology has undergone significant advances during the last decade. Tubing-conveyed perforating, underbalanced perforating, high-shot-density guns, better shaped charges, and improved gun systems have contributed to safer operations and improved productivity of the perforated completions. A recent development described in this paper is a perforated completions. A recent development described in this paper is a perforating tool that makes real-time downhole measurements [including perforating tool that makes real-time downhole measurements [including pressure, flow rate, temperature, gamma ray, casing-collar locator (CCL), pressure, flow rate, temperature, gamma ray, casing-collar locator (CCL), and cable tension] during a perforating run and can selectively fire a number of guns at different depths or times. In addition to providing better control of the perforating process, the simultaneous downhole measurements can provide in a single trip a production log, conventional well tests before and after perforating, and a fill-up or slug test soon after perforating for underbalanced conditions. Thus, the completion can be evaluated in real time and any needed remedial reperforating can be performed while the gun is still in the hole. Other applications include limited-entry perforating, monitoring of bottomhole pressure (BHP) during minifracture jobs, better depth control with a gamma pressure (BHP) during minifracture jobs, better depth control with a gamma ray detector, fluid-level monitoring, and underbalance control. The applications of these measurements, with field data obtained with the Measurement While Perforating (MWPSM) tool, are the subject of this paper. Examples show the capabilities and the versatility of the MWP tool. Introduction Gun perforating has been used successfully as a well-completion method for the last 50 years. Many developments in perforating technology have occurred to facilitate creation of a clean flow channel between the reservoir and the wellbore with minimum damage to the producing formation. These new developments have resulted in better productivity of the perforated completions and in safer, more economical perforating operations. Perhaps the most important development is the use of underbalanced conditions. When a formation is perforated underbalanced, the sandface is suddenly exposed to the lower pressure in the wellbore and the formation fluid enters the wellbore with a high initial surge. This leads to an effective cleanup of the damage caused by drilling and perforating and results in higher well productivity. The underbalanced perforating technique results in better completions under a variety of conditions. Fig. 1 shows typical underbalanced perforating setups for through-tubing and tubing-conveyed techniques. With the advent of tubin conveyed perforating, underbalanced perforating has gained acceptance as the technique for obtaining better productivity than with other techniques. With underbalanced conditions, the formation begins to flow immediately after perforating and the record of pressure and flow rate during the fill-up period can be analyzed as a pressure and flow rate during the fill-up period can be analyzed as a transient well test. Many variations of the well conditions are possible during the fill-up period: a well can be open or shut-in at the possible during the fill-up period: a well can be open or shut-in at the surface, it may or may not flow to the surface, and the test could be complemented by one or more stabilized-rate tests and buildups. In each case, however, a quick computer analysis can be done at the wellsite, which results in significant time savings, particularly for low-permeability reservoirs containing highly viscous oil. A large number of variables (formation heterogeneities, damage from drilling/cementing, chemical incompatibilities between completion and formation fluids, emulsions, etc.) affect the completion process. Therefore, well completions seldom perform as expected. process. Therefore, well completions seldom perform as expected. Each completion must be evaluated to confirm its efficiency and to determine the remedial actions needed. Traditionally, completion evaluation has been expensive and time-consuming, involving at least 1 or 2 days of well testing and production logging, and so often was bypassed. The MWP tool combines the execution and evaluation phases of the completion process. It provides production-logging/well-testing measurements during a perforating production-logging/well-testing measurements during a perforating run an pressure, temperature, and flow-profile measurements before and after perforating. It is no longer necessary to make another trip for production-logging information after a perforating operation. MWP Tool Description The MWP tool consists of a perforating cartridge, a pressure/ temperature sonde, a continuous flowmeter sonde, a scintillation gamma ray detector, and a flex joint (Fig. 2). The perforating cartridge controls selective gun firing and recording and transmission of information from the sensors to the surface. It also has a collar locator for depth control. The sensor sonde contains two temperature sensors and a strain-gauge pressure sensor having a pressure rating of 10,000 or 20,000 psi [69 or 138 MPa] with 0.15- or 0.30- psi [1.03- or 2.07-kPa] resolution, respectively. One temperature transducer measures the borehole temperature; the other accounts for the changes in the strain-gauge calibration resulting from temperature variations. The gamma ray detector is used to correlate with openhole logs and for depth control. The flex joint, which is located between the perforating cartridge and the gun string, helps absorb the shock from a fired gun string. Up to 30 guns can be included in the gun string, and any gun can be selected for firing regardless of its location in the string. Because the conductor through a gun is destroyed when the gun fires, the normal operation is to fire guns from the bottom up. The tool can be used for wireline-conveyed (through-tubing) perforating or tubing-conveyed perforating systems. The tool has a telemetry system to communicate perforating systems. The tool has a telemetry system to communicate with a surface computer and uses control pulses to communicate with the switches between guns. The switches are electronic and provide skip-over and gun identification. provide skip-over and gun identification. Well Testing With the MWP Tool Perforating with underbalanced pressure provides an opportunity Perforating with underbalanced pressure provides an opportunity to test the well immediately upon shooting. The MWP provides a continuous pressure (and, under certain conditions, flow rate) record during a perforating run, and the telemetry system allows us to monitor these measurements at the surface. These measurements give clues about what is happening downhole during the perforating process and can be analyzed as a pressure-transient test perforating process and can be analyzed as a pressure-transient test for transmissivity and skin. Fig. 3 shows atypical pressure and flow response after perforating. The situation is analogous to the drillstem ("slug") perforating. The situation is analogous to the drillstem ("slug") test (DST) where flow is initiated by opening a valve in the DST string. After the initial high spurt rate, the flow rate declines as a result of the increase in the backpressure on the formation caused by the rising fluid column in the wellbore. SPEPE P. 83