Frac packing has become the standard sand-control completion technique for many deepwater operators because of low completion failure rates and excellent production performance. These treatments are engineered to optimally place the stimulation fluids and proppants based on gravel- pack (GP) tool operational procedures and fracture model simulations. Direct near-wellbore measurements from radioactive (RA) tracers can be used to help minimize both engineering and operational uncertainties of this process.
A comprehensive review of 30 Gulf of Mexico frac-pack completions within four deepwater fields has been completed, in which RA tracers have been used. These logs allowed initial assessment of the sand control and resulted in better frac-pack designs. The average perforation length of these 30 completions is 94- ft and the average deviation is 41°.Three of these wells have more than 200- ft of perforations and seven have over 60° of hole deviation.
Stimulation fluids and proppants have been traced for years; however, the introduction of tools that differentiate between multiple isotopes and determine their position with respect to inside or outside the wellbore has improved the utility of gravel-pack tracers. The final location of the various fluid stages pumped during a gravel-pack operation is valuable information. With this knowledge, the completion can be accessed for reliability of sand control and productivity (including unwanted fluids). Modifications can be made to achieve completion design objectives of future completions.
This paper presents a number of case histories that document the utility of frac-pack tracers and focuses on the qualitative analysis of tracer logs. These examples show how costs have been reduced by operators learning when to pull a pack because of inadequate sand control, and when to perform a single treatment over a long or separated pay interval. Examples also show how service tool process changes were needed to eliminate sand sloughing caused by swabbing effects. Many other examples are discussed in the paper.
Well reliability has been improved by changing stimulation design and sand-control operational processes that lead to an incomplete pack. This insight came gradually over 5 years as processes were refined and additional information was acquired.
The gamma ray tracer logging tool runs on battery power and records data into memory chips so that a log may be obtained without a direct electrical connection to the surface Usually, for gravel-pack operations, the 1 11/16-in. OD logging tool is programmed, and a gauge hanger is used to secure the tool inside the washpipe, as shown in Fig. 1. In addition to this logging tool, multiple washpipe pressure and temperature gauges are often spaced out across the completion interval adjacent to areas of interest. The advent of the washpipe-conveyed technique has saved rig time and delays in first-well production. Also, one or more RA markers are placed in the gravel-pack assembly to improve the final log's depth accuracy. An alternate method for running the logging tool below the washpipe, when the washpipe is smaller than 2 1/16-in. OD, was never used during our deepwater operations.