Oil wells are built by drilling into rock. Special equipment destroys layers of rock and forms a hole, through which minerals are later extracted. Rock particles (sludge) get flushed from the well with the help of a drilling mud, which washes out all the excess under high pressure. However, due to the fact that formations contain various cracks, the liquid often goes into the cracks instead of rising up the well. As a result, the formation absorbs a large volume of drilling mud. Oil workers call a significant loss of drilling mud a catastrophic absorption.
As a rule, catastrophic areas are insulated with liquid cement. However, the latter spreads strongly under the action of gravity, leading to high cement consumption and increased repair costs. An alternative is the use of so-called cross-linked polymers, the molecules of which form a dense structure when interacting with each other. Although cross-linked polymers create an elastic gel without water loss, the hardened structure of the gel gets destroyed under pressure. Thus, none of the previously known insulating compositions could ensure that catastrophic absorption areas get blocked.
The scientists from Perm Polytechnic University have proposed to solve this problem by using a mixing plugging insulation material: a combination of cement and a cross-linked polymer. After mixing, the composition undergoes three phase transitions: it is pumped into the well as a liquid and moves through the drill pipes in the same state. At the bottom of the column, cross-linking occurs, and the composition enters the absorption area in an elastic state, which prevents it from spreading through the fractured cavity. After this, the material hardens and gains strength, which allows it to withstand the hydrodynamic pressures that arise at further stages of well construction.
“The requisite properties are achieved by using a basic composition (cement, confining liquid, functional additives) and a polymer. This combination allows us to obtain a homogeneous mixture, the density and thickening, time of which can be chosen in accordance with specific geological and technological conditions by adding conventional additives to cement, such as retarding reagents,” Alexander Melekhin, candidate of technical sciences, is quoted as saying by Perm Polytechnic University.
