The Importance of Sand Characterization for Efficient Well Completions | Absolute Completion Technologies
By ‘an efficient well completion’ we intend a design that enables the well to produce optimally for a long period of time. Efficient completion designs will recover the maximum reserves while requiring minimal remedial intervention to the well. The planning must begin at the same time as planning for the drilling begins.
Over the past decade, operators worldwide have taken advantage of the rapid advances in horizontal drilling to create longer and longer lateral wells. Many horizontal wells today intersect several kilometres or more of reservoir. Unlike vertical wells with relatively short exposure to the pay zone, rock characteristics can vary greatly along the length of a horizontal well.
Advances in well completion technologies have lagged improvements in drilling capabilities. To some extent this is because the production problems inherent with horizontal wells are only now emerging and starting to be studied and understood after a few years of well production. In addition, engineers are learning that carrying out the type of remediation work common to vertical wells is extremely difficult and expensive, even impossible, in horizontal wells.
The mobility of solids in the near wellbore area can prohibit long term, efficient well productivity. This problem will arise early in a well’s life in less consolidated reservoirs, but it is estimated that a large majority of wells, in excess of seventy-five percent, will begin to mobilize solids as fluid is produced over time.
The following problems can be exacerbated when no sand control is implemented in the initial completion of unconsolidated rock formations, and/or over time with increased well draw down:
- frac sand flow back;
- formation sands flowing into the wellbore, settling, and inhibiting hydrocarbon flow;
- plugging of the near wellbore/sand screen interface due to formation fines and/or residual drilling muds not removed from the wellbore;
- high flow velocity induced hot spots, erosion or jetting of the sand control medium, which eventually allows solids to produce into and build up in the wellbore; and,
- breakthrough or preferential production of water, steam or gas due to well plugging
These problems can be avoided with proper initial well completion designs that are based on sand characterization. An efficient completion design will effectively control sand while promoting hydrocarbon inflow. The well completion must perform optimally for the life of the well. To achieve those goals, completion engineers must do two things:
- understand the operating principles of various sand control technologies; and
- plan to carry out sand sampling across the reservoir during the drilling phase, preferably by coring.
Analysis of the samples will characterize the formation rock and reveal how it changes across the lateral wellbore. The most important factors that make up sand characterization include:
- Particle size distribution;
- Concentration of fines (particles under forty-four microns in size);
- Hardness of the rock;
- Sphericity and shape of the particles; and
- Mineral composition.
The reason sand characterization is so important is that the effectiveness of many sand screen technologies depends on the sand particles forming arches or bridges at the sand-screen interface. When sands are relatively coarse and uniform in size distribution, most screen technologies can be effective.
However, gap size dependent products such as wirewrap, slotted liner and conventional weave premium screens must be sized based on valid sand samples that truly represent the formation. Accurately sizing gap based screens becomes more challenging with horizontal wells that pass through formations that can vary considerably from zone to zone. Accurately sized gap based screens promote the formation of stable arches. The arch structure blocks other sand particles and allows fluid and fines to pass between the particles and through the screen into the wellbore.
When gap based screens are not sized properly or the particle size distribution is highly varied, selecting an appropriate screen size can be very difficult. Pumping and flow changes will cause unstable arches to collapse and larger particles will eventually plug the screen, block flow and cause high pressure hotspots that can lead to screen erosion.
More recent developments in screen technology, such as Absolute’s MeshRiteÔ and Tri-D WeaveÔ filter media, do not rely on a gap structure or gap sizing to control sand. These wire mesh and special weaves form three dimensional pores of variable sizes that are very effective at controlling sand while retaining high retained permeability at the sand-screen interface.
In conclusion: When sand sampling is not performed the risk of losing the well over the long term increases. Remediating wells with failed screens, or no screen, is extremely difficult in horizontal wells. Sand characterization is the key to understanding which sand control technologies will be effective, and allowing engineers to balance completion cost with optimum well productivity.