The Real World isn't Perfect: An Investigation into Wellbore Clean-Up with Non-Uniform Filtercake Exposure

Abstract

Soft sand wells are typically more expensive completions due to the need for sand control. The cost of the wells makes the completions more high-risk and increases the need for laboratory testing to validate the screen or gravel pack sizing as well as drill-in fluid selection and filtercake cleanup. Dynamic drill-in fluid clean-up testing provides a state of the art methodology for determining the least damaging drill-in fluid and / or the most effective clean-up treatment for the filtercake. However, the test method to date, referenced in SPE 112497 and SPE 179024 has used a 100% uniform clean-up treatment approach. This approach has assumed that all of the clean-up treatment uniformly contacts and treats the filtercake. In the actual well, it is unlikely that 100% uniform clean-up exists. It is possible in the wellbore to encounter selective clean-up treatment leakoff due to permeability differences or variable filtercake thickness. This paper investigates the results when a less uniform clean-up environment is encountered. The dynamic drill-in fluid testing utilizes designed-for-purpose slot flow cells which allow soft sand formations to be confined and tested while still exposing the face of the formation directly to the drill-in fluid or clean-up treatment during the test. The well conditions are received from the client and the shear rate at the formation face is calculated and matched in the laboratory. The test simulates wellbore conditions as closely as possible including annular shear rate during filtercake deposition, overbalance pressure, temperature and multiple clean-up flushes. In this study, the amount of filtercake clean-up treatment fluid loss was modified to simulate multiple effective clean-up scenarios. Additionally, testing was completed on aloxite discs in a standard HPHT fluid loss cell in order to provide a comparison between the dynamic and static tests. The dynamic fluid loss testing has been designed to match treatment volumes and conditions in the actual wellbore as closely as possible. The assumption that 100% uniform application of the clean-up treatment contacting the filtercake has always been the basis for the testing. However, changing the previous assumptions to allow for non-uniform application of the clean-up treatment during the testing provides another opportunity to challenge our perceptions and simulate the actual well more completely. The modification of the standard test procedure to allow the simulation of non-uniform clean-up of the filtercake in the wellbore adds further to our understanding of the actual wellbore clean-up. The relationship of the results between the static and dynamic fluid loss provides an opportunity for pre-screening work to be conducted and related to the final results achieved in the dynamic fluid loss test.

A Well Flux Surveillance and Ramp-Up Method for Openhole Stand-Alone Screen Completion

“…The casing or liner is set above or inside the producing formation. The completion interval is drilled using a drill-in fluids (DIF) or reservoir drilling fluids (RDF) that is optimized for drilling and filter cake cleanup (Fischer et al, 2018. The interval is open or uncased and has only screen for sand control.…”