Conventional slurry packing methods involve a screen and from 120' to 160' (36.5m to 48.7m) of blank pipe above the screen. The blank pipe acts as a sand pipe above the screen. The blank pipe acts as a sand reservoir for the gravel pack screen. Sand settles after the gravel pack is completed and after the gel breaks. To help ensure a good gravel pack job in a well that has less blank pipe than screen, a multiple stage slurry pack process was designed along with a multiple stage crossover tool.
A well was recently completed offshore Louisiana in three zones. (Fig. 1). The top two zones (zones B and C) were gas reservoirs and the bottom zone (zone A) was an oil reservoir. Zone A was the only reservoir that required sand consolidation as was determined from two offset wells and it was decided to gravel pack zone A. Separation between zone A and zone B was 30' (9.1m) (Fig. 2) which ruled out conventional high density gravel packing procedures. To gravel pack the well a new procedure was developed using a multiple stage slurry pack, a crossover tool, and acid to break the gel in the sand slurry. By utilizing this procedure the well could be completed as a dual flowing well. This procedure is called the "short-lap" gravel pack (Fig. 3). At the time this job was performed, it was the first time the procedure was known to have been used. procedure was known to have been used.
The short-lap gravel pack is a high density gravel pack with limited blank pipe, i.e., gravel pack reservoir. In this case only 7' (2.1m) of blank pack reservoir. In this case only 7' (2.1m) of blank was available for the sand reservoir. Normal gravel packing techniques call for approximately 3 times as packing techniques call for approximately 3 times as much blank pipe as screen. (Fig. 4) In this case the blank screen would have been 120' (36.5m) with 40' (12.2m) of screen.
In normal high density gravel packing procedures, the sand will settle to 60% of the original volume in the blank pipe or sand reservoir. The slurry is also assumed to dehydrate between the screen and perforations. To ensure that no voids were present in the perforations. To ensure that no voids were present in the sand reservoir HCl acid was spotted inside the screen and forced into the formation to break the gel. To do this a tool was devised to place the acid inside the screen. The crossover tool was designed to perform the following operations: perform a squeeze pack, circulate fluids inside the gravel pack screen, circulate fluids above the gravel pack packer, and reverse excess sand slurry from the well. By being able to place the HCl acid inside the screen and forcing the acid into the perforations to break the gel, the sand was able to settle and fill any possible voids in the screen. Once the gel was broken with acid another sand slurry was pumped to replace any sand that settled behind the blank pipe. In addition to this process, screen was used in place of blank pipe (Fig. 3). This was done to aid in dehydrating pipe (Fig. 3). This was done to aid in dehydrating the sand that was to be used as a sand reservoir.
Critical to the success of this job was a crossover tool as presented in Fig. 5. This crossover tool was designed to be placed in 4 positions during the slurry pack operation. Position one, called the "weight down" position, is used for squeeze operations. In this position the sand slurry is circulated down between the casing and screen. Once a pressure increase is seen due to the slurry dehydrating across the tell-tale screen, the hydril is closed to prevent returns. The sand slurry is then forced into the perforations. perforations. The second position, called "tension", is used for circulating through the screen. This position is used for the second and subsequent slurry packs. After the initial slurry pack was done and the HEC carrying fluid was broken with HCl acid, the second and third slurry packs were done. Returns were taken from the casing through the screen in this position. By taking returns through the screen gravel was not forced into the perforations and the sand slurry was dehydrated.