Paper: A Gel Diverting Agent Used In Acidizing Treatments

Diverting methods have been developed and used extensively to distribute treating fluids in a zone or to divert them from one zone to another. Diverting may be accomplished mechanically or chemically. Mechanical diverting with perforation-sealing balls is a common procedure, but conditions may exist which make it ineffective. The height of the zone, number of perforations, limited pump rate, and capacity of the formation to take fluid are factors which may lower fluid velocity so that it is not adequate to seat the balls on the perforations. Communication between perforations or behind the casing, or perforations that are not round also may limit the effectiveness of ball sealers. for an impermeable gel diverting system was recognized. A gel diverting system, in order to be used as a diverter in acidizing treatments, has to meet the following criteria: the gel has to have a low viscosity during placement, hydrate to form a solid impermeable gel in the formation, revert with time to a liquid for removal, and leave a minimum of permeability damage. Packers also have provided effective mechanical diverting. However, they are more difficult to use because their effectiveness is dependent on accurately locating the zone to be treated and accurately setting the packer to isolate this zone. Numerous soluble particulated solids, which are often referred to as temporary bridging agents, have been developed for fluid diversion. These are solid chemicals that have varying physical and chemical properties. An agent can usually be selected that is satisfactory for a specific treating operation. These diverting agents usually are transported in a viscous carrier fluid and are pumped between stages of treating fluid. The effectiveness is dependent on the strength and permeability of the bridge formed. Some solid diverters have a wide particle size distribution and form low permeability bridges, but their permeability is not, low enough to effectively divert treating fluids to zones having a permeability less than about 2 md, and the need Various chemical types of gelling agents were evaluated in order to obtain a feasible gel diverting system. On the basis of the gelation time and stability tests, only two gelling agents appeared to meet the necessary criteria. One of these gelling agents was a high-residue natural gum and the other was a low-residue modified natural gum. A gel diverting system using the low-residue gum was finally selected since the diverting-efficiency and permeability-recovery tests showed that using the high-residue gum resulted in permeability damage. So, only the data using the low-residue gel system are presented in this paper, except in the diverting efficiency and permeability-recovery tests, in which case the data from tests using both the high and low residue gums are presented. The procedure used on a field job is presented, and the results are described.