Abstract
Water soluble organic polymers such as hydroxethyl cellulose have been used to slow the leak-off rate of clear brines into permeable formations. Fluid loss or leak-off, however, can only be effectively controlled by bridging the pore openings with rigid or semi-rigid particles of sufficient size and number. Production engineers have been reluctant to use particle bridging because of the possibility of particle transport into the formation resulting in formation damage and/or costly and often ineffective stimulation treatments. A particle bridging fluid has been developed that quickly and effectively controls fluid loss in a wide range of permeabilities and pore diameters. The filter cake formed in this process, however, is highly dispersible to the produced fluid and thus effectively removed by placing the well on production. No acid treatment or other removal techniques are required.
The primary bridging agent in this fluid is a sized calcium carbonate with particle sizes (Fig. 1) capable of initiating bridging in pore diameters in excess of 100 micro meters. The particle size distribution also compliments the smaller openings created during the filter cake formation process, thus assuring that fine particle transport into the formation is minimized. This external bridging has been documented by Scaning Electron Microscopy, Cross sections of a dynamic filter cake obtained at elevated temperatures and pressure were examined under the SEM, shows sharp delineation between the cake and filter media. That is there were no significant calcium carbonate particles transported into the filter media pores. This property greatly enhances filter cake removal on back flow and thus provides for good return permeabiltity.
Water soluble organic polymers are added to provide rheological and filtration control for the fluid system. The filtration control polymers are sufficiently flexible and deformable to fill the small irregular pore openings of the final particle bridge and thus provide positive leak-off control for the fluid. Since the calcium carbonate particles will settle in water or even high to decrease adhesion of filter cake particles thus greatly enhancing the dispensability of the cake. By utilizing this technique, the filter cake can be more effectively removed from the sand face by the produced fluid.
Water soluble organic polymers such as hydroxethyl cellulose have been used to slow the leak-off rate of clear brines into permeable formations. Fluid loss or leak-off, however, can only be effectively controlled by bridging the pore openings with rigid or semi-rigid particles of sufficient size and number. Production engineers have been reluctant to use particle bridging because of the possibility of particle transport into the formation resulting in formation damage and/or costly and often ineffective stimulation treatments. A particle bridging fluid has been developed that quickly and effectively controls fluid loss in a wide range of permeabilities and pore diameters. The filter cake formed in this process, however, is highly dispersible to the produced fluid and thus effectively removed by placing the well on production. No acid treatment or other removal techniques are required.
The primary bridging agent in this fluid is a sized calcium carbonate with particle sizes (Fig. 1) capable of initiating bridging in pore diameters in excess of 100 micro meters. The particle size distribution also compliments the smaller openings created during the filter cake formation process, thus assuring that fine particle transport into the formation is minimized. This external bridging has been documented by Scaning Electron Microscopy, Cross sections of a dynamic filter cake obtained at elevated temperatures and pressure were examined under the SEM, shows sharp delineation between the cake and filter media. That is there were no significant calcium carbonate particles transported into the filter media pores. This property greatly enhances filter cake removal on back flow and thus provides for good return permeabiltity.
Water soluble organic polymers are added to provide rheological and filtration control for the fluid system. The filtration control polymers are sufficiently flexible and deformable to fill the small irregular pore openings of the final particle bridge and thus provide positive leak-off control for the fluid. Since the calcium carbonate particles will settle in water or even high to decrease adhesion of filter cake particles thus greatly enhancing the dispensability of the cake. By utilizing this technique, the filter cake can be more effectively removed from the sand face by the produced fluid.
Extensive testing of this fluid composition has been conducted in a high pressure-high temperature return permeability apparatus. In this test an initial oil permeability is established to a sand pack as shown in Fig. 1. The leak-off rates and percent return permeabilties for three different weight systems are given in Table 1. As will be noted these range from 66 to 82% return. These test are based upon 250F and 500psi differential pressure.. Mud off temperatures below 200F will show much higher return permeability. Note also that the bridged solids must also be produced through the 40/60 gavel pack sand or be displaced into the sand porosity so as not to greatly affect the overall permeability.
Over 50 wells have utilized this bridging system to control fluid loss to the formation with good success and in each case production has been equal to or better than expected. Neither has it been necessary to acidize or utilize other stimulation techniques. A typical application and results ae exemplified by the following case history. The subject well was designed for perforating from 11,452 to 11,560 ft, pulling the guns up above the perforation, pre-packing and killing operations, however, failure to set the packer after perforating resulted in the well taking 35 bbl./hr kill fluid losses. Ten barrels of the bridging fluid was prepared and pumped into the well which reduced fluid losses to zero. The perforating guns were tripped out of the hole, and a staged acid pack was performed. After gravel packing the well it began taking fluid losses at 35 bbl/hour. Another 10 bbl bridging fluid pill was pumped into the screen to kill the well After production equipment was run into the well, it was put on production and allowed to clean up. Subsequent well production rate exceeded the operator’s expectations at 10 MMSCFD, with a four percent drawdown.
On the basis of numerous successful field applications it can be concluded that the bridging technique used in this system can be used to effectively control fluid losses but yet be removed by the produced fluid without resorting to acidizing or breakers.
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