Abstract
Historically, a fracture treatment with proppant is performed with a dedicated workstring connected to downhole completion equipment (such as a permanent packer, a tubing seal receptacle (TSR), or a locator assembly). This paper discusses offshore field operations in Brazil to illustrate how surface and downhole equipment, including a temporary completion string, were capable of meeting these challenges for hydraulic fracturing using ceramic proppants, followed by an acid job before a drillstem test (DST), which saved at least 6 days of rig time.
When performing a DST with a temporary completion string, there are risks associated with using this type of fracturing treatment these mechanical tools can lock up if they are operated with proppant still packed in the operating sections (such as the tester valve and circulation valve). It is recommended that during the job the tool operation should be minimized to the absolute minimum because proppant can be packed in other areas of the tools. Halliburton performed extensive testing before the operation to determine the erosional limits of the DST tools; as a result of this testing, the maximum flow rate of the fracturing process was limited to 23 bbl/min. In this treatment, debris-tolerant valves, rather than standard valves were used. The debris-tolerant valves were specifically designed and tested to manage more debris.
The well-test surface equipment was made of a solid-tolerant design, including a choke manifold (high abrasion tolerance), a four-phase separator, which was used to separate the solids, and surge tanks that are suitable for managing well flow that contains solids. Additional atmospheric tanks were provided in the test plant as part of a contingency plan to store fluids in the event of a high concentration of solids or/and untreatable fluid, which cannot be discarded or burned; sensors for solids were installed downstream from the choke manifold.
During the hydraulic fracturing operation, 2,760 bbl of fracturing fluid containing the 20/40 mesh size proppant was pumped at a rate of 23 bbl/min with a maximum concentration of 6 lbm/gal. During the fracturing job, a screenout occurred, and the contingency plan was followed, removing most of the proppant inside the string. The well-testing plant received 130 bbl of the fracturing fluid at the surface during the cleanup of the well. The DST tools were fully functionable after the fracture treatment, and the test was successfully performed.
The main objectives of well testing included the characterization of the reservoir (primarily, all variables to calculate the productivity index and the reservoir fluid (specific gravity (SG) of oil and gas/oil ratio (GOR). A stimulation technique is commonly used to increase the PI, and in some cases, with exploratory wells, the stimulation and well testing are combined to gather information to determine the effectiveness of the technique and whether or not this method is sufficient to make the block lucrative. One of these stimulation techniques is hydraulic fracturing, which is a process that pumps fluids down a well at specific rates and at pressures sufficient to create fractures in the formation. A support agent, in this case the proppant, is needed to keep the fractures open; proppant is usually made from a ceramic-type of material. The proppant is transported by the fluid to fill the resulting fractures. Another characteristic required by the supporting agent is a well-controlled geometry and size that will not hamper the flow of the hydrocarbons.
