Wells with sand control measures may still exhibit onset of sanding during production, often due to isolated damage of individual screen sections. Positive identification of the location of the sand production allows targeted mitigation to remove the sanding source while retaining as much hydrocarbon flow as possible. This paper discusses the novel acoustic techniques used to identify productive zones and areas of sand production in a well suffering a sanding event.
Ultrasonic methods for sand detection in a downhole environment have proved troublesome primarily due to the difficulty in separating acoustic signatures due to particle impacts from those generated by turbulent flow. Advances in sensor technology and digital sampling have enabled reliable discrimination of turbulence and particle signatures in both controlled flow-loop conditions and in real producing wells. Novel processing algorithms have been developed to not only detect sand ingress points, but also to quantify and characterise sand particles in the flow stream.
A horizontal oil producing well exhibited a change of behaviour following an increase in choke opening, when it started to produce sand along with an increased water cut. A toolstring combining production logging, acoustic sand detection and multifinger caliper with a tractor for conveyance was deployed in the well and a number of passes were made combining continuous logging and stationary recordings. The acquired data indicated there was no crossflow during shut-in, while there were indications of sand build-up over the lower sections of screens. With the well flowing, the PL data showed the inflow profile across all screens and identified a point of very large influx of mostly water. Analysis of the acoustic data using transient statistical sampling techniques showed this to be the main source of sand entering the wellbore and was able to verify sand transport in the flow stream. Analysis using general noise level sampling was able to detect energy due to turbulent flow in and into the wellbore, correlated with spinner responses, and also in the near wellbore environment behind certain screens. Multifinger caliper data confirmed the general integrity of the screens and enabled the planning of isolation measures to shut off sand production while minimising production loss.
The verified ability of the new tool to separate the acoustic signatures of particle impacts from turbulent flow noise brings an additional aspect to production logging interpretation, allowing inflow profiling for solids as well as fluid phases. Statistical analysis of the broad-spectrum noise recorded also reveals information about fluid flow not just in the wellbore but also in the near-wellbore environment behind the primary tubular. This information can prove critical in analysis of completion design.