Workover fluid for the reconstruction of wells with reduced reservoir pressure

Creation of back pressure on the deposit and prevention of damage to the wellbore zone is the basic task of the workover fluid of appropriate density, pumped into the well to carry out the required scope of reconstruction work. The composition and technological properties of the workover fluid should be determined based on the current geological and reservoir conditions in the given well or pay zone. Well reconstruction liquids used in reservoir conditions are brines without a solid phase and prepared based on brine with the addition of among others a polymer and a blocker. They are used in wells where a fluid density of 1.03–2.3 kg/dm3 is required to balance the reservoir pressure gradient 0.00981–0.023 MPa/m. However, in deposits where the gradient of reservoir pressure is below 0.00981 MPa/m, special liquids with a density of ≤1.0 kg/dm3 should be used. Preliminary laboratory tests carried out at INiG – PIB showed the direction of selection of agents constituting the base of such fluids and the impact of these agents on the technological properties of the obtained workover fluids with a density of ≤1.0 kg/dm3 . Research has shown that these can be synthetic compounds that act as oil and do not contain aromatic hydrocarbons that are harmful to the environment. This group of compounds includes esters, polyalphaolefins, ethers and acetals, and esters and chemical compounds from the olefin group have gained the widest use in drilling fluid technology. The subject of laboratory research on the development of workover fluids for deposits with reduced reservoir pressure was a synthetic chemical compound acting as an oil, i.e. fatty acid methyl esters rapeseed oil. Using this compound, laboratory tests were made to prepare fluids that constitute two phases, i.e. oil and water. The tests that were carried out for geological and reservoir conditions occurring in the Carpathian Foredeep wells included determining the composition of the oil and water phase, the method of preparation of these fluids, determining their technological and inhibitory properties as well as the impact on the environment.