Sand control in horizontal wells
The evolution of sand control from historical water wells to recommendations for 15,000 ft+ horizontal oil/gas wells.
This summary article backgrounds the need for formation sand entry prevention in downhole producing wells from man's first dumping of rocks into water wells drilled with rock or iron tools. Thousands of years later, the oil/gas industry invented basic gravel pack and sand screen methods to prevent inflow of unconsolidated formation sands. Now the drilling of horizontal boreholes over 15,000-ft long has created ever new challenges and need for sand control in extremely long sand intervals.
The discussion covers this story with: 1) A historical review; 2) Basic barefoot, gravel pack and stand-alone screen completions; 3) Selecting sand control type for a horizontal well; and 4) Innovation for future use.
HISTORY OF SAND CONTROL
Way, way back, when early humans needed water, they dug water wells with their hands. Then they needed more water, so they began using tools to drill into sand beds. They found that they could work faster and go deeper by using a heavy rock or iron as a percussion tool, like a yo-yo, to cut through to the water bearing sand.
Water-well technology. Sand problems were born. Loose sand was coming up with the water or falling to the bottom of the well, stopping the water flow. They were able to prevent the problem by filling a small part of the well with large rocks.
Much beyond the rock-dumping era, better ways to stop sand production and maintain high water production rates were developed. By the late 19th and early 20th centuries, they cut holes in liners to stop sand production, and later found they could drop gravel down the annulus to form gravel packs that gave even better results. Oil companies quickly modified sand control techniques to handle deeper and dirtier wells.
Oil industry advances. Perforated liners were popular in the early 20th century, without much concern about the sizes of perforations to be used. Then academia jumped on the oil wagon with such people as C.J. Coberly, who published his work on "Selection of screen openings for unconsolidated sands" in 1937. 1 This was a starting point for technical means of designing sand control tools.
Great improvements were developed by the oil/gas industry despite politics and prejudices. Some of the major sand control techniques developed during the second half of the 20th century were: sand consolidation, slotted liners, wire wrapped screens, prepacked screens, premium screens, gravel packs, frac packs, high-angle-hole gravel packing and horizontal-well gravel packing.
The most challenging of these has been controlling sand in horizontal wells, as drilling technology is now able to drill to distances of more than 15,000 ft from heel to toe. For the uninitiated reader, "heel" is the beginning of the horizontal wellbore and "toe" is the end of the horizontal wellbore.
CONTROLLING SAND IN HORIZONTAL WELLBORES
Regarding barefoot completions, the simplest and least expensive completion is to put a well on production without anything left in the productive interval. Without casing, liner, screen or tools therein, we rely on the sandstone being strong enough, and shale beds stable enough, to resist changing pressures as the well is depleted. This works very well in strong sandstones, dolomites and limestones, but will fail in weaker sandstone, or where there is tectonic activity.
Sometimes it is impossible to understand why sand begins to be produced from a very strong sandstone, but the most common cause is the onset of water production. There may be a chemical reaction between extraneous water and natural cementing agents of the oil bearing formation. This should always be tested and anticipated by core tests.
One barefoot completion in a horizontal well off Western Australia began producing sand after a year or so of production, and it was...
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