The Sanding of Oil Wells

Excepting the very few oil fields of the world in which the production comesfrom a limestone formation, the greatest problems encountered in oil wells comefrom trouble caused by sand. These troubles are brought about by sandaccumulating in the strainer, liner, tubing, or cutting out various parts ofthe well equipment. The remarks here made are intended to apply to theso-called "soft sand" producing areas such as those of California andthe Gulf Coast of Texas and Louisiana. However, there are certain features ofsanding problems in pumping wells which are almost universal. In the "soft sand" producing districts such as California or the Gulf of Texas and Louisiana, wells often come in flowing at the rate of severalthousand barrels of oil per day, and after flowing a few hours, "sandup." In many cases it will be found that when the sand is cleaned out ofthe strainer or liner, and the well again starts flowing the production will bebut a small fraction of what it was originally. Many and varied opinions havebeen handed down by oil men to account for this condition. The most satisfactory explanation of this failure of wells to come back toinitial flow, after once sanding, will be found from a close study of theproducing formations. It will usually be found that the oil-producing zoneconsists of alternating layers of sand and shale. In the Gulf Coast districtthese alternating layers may be only a few feet or a few inches thick. When thewell blows out or starts to flow with an accompaniment of strong gas pressurethe sand is blown into the hole through the screen, strainer, or perforatedpipe. Large quantities of sand quite commonly accompany these flows. Theholding of back pressure on the wells by use of "flow beans," etc., tends to hold back the sand. Also the use of fine-gage screen helps to hold thesand back; but if the pressure is very strong and the gas is present the screenis usually cut out in short order. The explanation of the failure of the well to "come-back" afterbeing cleaned out, consequent to the initial sanding up, will be found back ofthe liner or screen.