Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.
A temporary diverting agent must work in a dynamic environment comprised of high fluid flow velocities, relatively high pressure differentials, liquids of differing solubilities and possibly high temperatures. Naively, we have often ignored this dynamic situation and merely dumped solids into fluid streams expecting, and partially realizing, blocking to occur. An evaluation of what is involved in forming a nearly impervious mass and introducing it into a fracture was undertaken. An apparatus was designed and built to prove theories developed from engineering and chemical considerations. The apparatus allowed high flow velocities and high pressures to combine in hurling likely candidate materials into a variety of simulated fractures. The laboratory tests confirmed that a well graded formulation of solid materials produced spectacular blocking results. These laboratory test results have also been confirmed by many highly successful field jobs.
For many yearn solid materials have been used down hole as-temporary barriers for diverting injected fluids. A typical operation involves adding the solids to a carrier fluid which is then pumped down hole. This solid laden fluid will be pumped into existing fractures and fissures. As the solids lodge and wedge in the openings and cracks within the formation, they reduce the flow, thus, increasing the back pressure. As the flow decreases due to the pressure. As the flow decreases due to the action of additional solids blocking the fluid path, the pressure continues to rise until path, the pressure continues to rise until another region of the formation fractures and provides a different path for the fluid to follow. provides a different path for the fluid to follow. The treating fluids with proppants, etc. will then act on this new untouched region creating new channels of greater permeability so that the well will produce from additional zones.
After treatment has been completed the blocking agent should be forced out of the formation and up the well to the surface by a combination of formation pressure and dissolution by some combination of temperature, bacterial or enzyme action as well as the production fluids; crude oil, formation water, or gas. Thus the blocking agent disappears and all zones contribute to the wells' production. While some successes have been experienced in this simple operation, many unexplained failures have occured. This situation prompted an investigation into the mechanics of blocking fractures.
PHYSICAL FACTORS PHYSICAL FACTORS The factors which are of concern in sealing fractures with solids are primarily physical. What is desired is merely a small dam across openings in the formation.
The fractures in the formation are blocked by first having a bridge formed by the larger particles, and then smaller particles building up on particles, and then smaller particles building up on them. Since fissures could range from 1/10 to 1/4 inch in width (and greater), a range of particles up to about 1/4 inch is required to form particles up to about 1/4 inch is required to form the initial bridged. The finer particles are necessary to plug the smaller holes around the bridged particles and the formation. The particle has to be hard enough to withstand the compressive loads of the formation "walls" and hydraulic pressure. pressure.