This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 189568, “Sand Production Caused by Water-Hammer Events: Implications for Shut-In Protocols and Design of Water-Injection Wells,” by Haotian Wang, SPE, Jongsoo Hwang, SPE, and Mukul M. Sharma, SPE, The University of Texas at Austin, prepared for the 2018 SPE International Conference and Exhibition on Formation Damage Control, Lafayette, Louisiana, USA, 7–9 February. The paper has not been peer reviewed.
A pressure pulse, known as a water hammer, can occur immediately after water-injection wells are shut in for emergency or operational reasons. Large pressure pulses may cause wellbore-integrity problems such as sandface failure and sand production. This paper proposes a new work flow to simulate water-hammer events, the resulting wellbore failure, and sand production in water injectors.
For water-injection wells handling high injection rates, water-hammer signatures are observed when water injection is stopped. Designing water injectors and deciding how quickly or slowly to shut in wells requires careful attention. Prediction of sand failure caused by water-hammer events can help design shut-in protocols for water injectors. The new work flow developed in this paper integrates water-hammer simulations with sand-stability and -production predictions. The water-hammer simulation shows that rate changes during shut-in affect water-hammer amplitudes and attenuations significantly. Large pressure fluctuations, or large amplitudes in the water-hammer signature after a quick shut-in, are shown to result in significant sand failure, and a slow shut-in procedure can minimize sand production. Sizing of well- completion components and location of subsurface valves are key in the design of injection wells and can be optimized to soften the effect of water-hammer events and associated sand production.
The authors evaluate the effect of water hammer on sand failure with numerical-simulation methods. Two numerical simulators—a water-hammer model and a sand-production-prediction model—are integrated.
Results and Discussion
Performance of an injection well can be affected by many factors. Suspended solids or oil droplets in injection water can plug the matrix near the sandface and form a filter cake on the sand at the wellbore. Research has shown that the injectivity-decline process is affected mainly by filter cakes and cross-flow between layers; this influence can be heightened by water-hammer pressure pulses during shut-in. The existence of water hammer, and its period, amplitude, and decay rate, varies depending on injection-well design and shut-in procedure.
Continuity and momentum-balance equations are solved for the fluid in the wellbore after shut-in of water injectors. Simulated bottomhole pressures (BHPs) containing water-hammer signatures are used as a boundary condition for the sand-production simulation. The input parameters for a vertical-well base case and a horizontal-well base case are summarized in Tables 1 and 2, respectively, of the complete paper. The wellbore trajectory of the horizontal well is assumed to have four sections.