Flood Management: Solving Conformance or Sweep Efficiency Problems—Part 3: Solution Performance Analysis
Authors: Smith David 
Published: August 2023

In Part 1 we covered the basic outline for conformance engineering practices with a focus on understanding the problem and how that impacts success rate. In Part 2 our focus was on making a connection between the problem type and the solution options available for dealing with conformance problems.

Part 3 looks at the importance of performance analysis and how to generate the economic benefit for solving conformance or sweep efficiency problems. The economic elements of this review are very basic, but they will help you to generate a more accurate understanding of the true economic benefit.

Job or Treatment Performance Analysis As discussed in Part 1, we often misunderstand the full or true nature of the conformance problem we are dealing with. This misunderstanding can often be corrected if we take a careful look at the post solution execution information.

In SPE 103044, we discussed how the first two solutions applied in the Permian Basin Anton Irish field which pumped 8,000 bbl of high-molecular-weight crosslinked gel, followed by 2,000 bbl of nitrified cement, only resulted in the maximum net pressure increase during pumping of 150 psi. This taught us that the features we were treating were much larger and more prolific than we originally expected. From this we improved the strength of our treatments and at the same time reduced costs by redesigning several elements of the solution process.

Another great example of utilizing treatment performance analysis was shown in SPE 190209 which solved a conformance problem in the offshore Ekofisk field in the North Sea. In this solution, we needed to confirm that we could execute the design without the need for a costly workover or drilling rig. We needed to confirm that we could pump approximately 3,000 bbl of nitrified cement through the existing completion without fear of locking up. Thus, in the planning phase of this solution treatment we pumped a densified gel designed to emulate the pumping of nitrified cement through the existing completion. Fig. 1 shows the pressure responses during that emulated treatment.

This plot compares the bottomhole pressure vs. the surface treating pressure during the period when the densified gel cement emulation fluid was pumped. The pressure scales have been shifted to eliminate the hydrostatic differential while pumping with water at 5.0 bbl/min. This allows us to look at the change in the curves to show the effect of the emulation fluids’ friction effect in the tubulars vs. the effect in the VSC (void space conduit) we were pumping into.

For the friction effect in the tubulars (4.5-in.-diameter with a capacity of about 240 bbl), we looked at the end of the job when we shifted from pumping densified gel to pumping water. Analysis of this section highlighted by the blue-shaded circle in Fig. 1 shows that the net friction pressure effect that was generated while pumping at 5.0 bbl/min with the densified gel in 4.5-in.-diameter tubing was approximately 1,160 psi. We can then compare this to the bottomhole pressure response, which basically represents the friction pressure response for pumping 3,200 bbl of densified gel into the VSC at 5.0 bbl/min was only approximately 500 psi.