Multielement compound saltwater drilling fluid

Abstract

The invention relates to a high-density multielement compound saltwater drilling fluid applicable to compound salt bed drilling. The high-density multielement compound saltwater drilling fluid comprises the following components in parts by weight: 100 parts of water, 15-50 parts of multielement compound salt, 1-15 parts of plugging agent, 2-8.2 parts of fluid loss additive, 0.1-0.6 part of pH regulating agent, 1-10 parts of lubricant and 1-270 parts of weighting agent. The multielement compound salt is a mixture of three or more than three of sodium chloride, potassium chloride, calcium chloride, sodium formate, potassium formate, cesium formate and sodium silicate. Due to the synergetic effect of the multielement compound salt and the plugging agent, the drilling fluid can be used for effectively sealing a well wall, meanwhile has favorable microcrack sealing capability, is capable of retarding drilling fluid filtrate transfer, has strong capability of retraining the dissolution of rock salt and gypsum and the expansion of evaporite and mud stock, and can be used for enhancing the well wall stability of an evaporite mud compound salt bed. When the density is up to 2.35g / cm<3>, the drilling fluid still has favorable rheological property and lubricating property, and can meet the requirements of straight well and directional well drilling of an evaporite bed.

Description

technical field [0001] The invention relates to a drilling fluid for petroleum drilling, in particular to a high-density multi-component composite brine drilling fluid suitable for drilling salt-gypsum layers, especially vertical wells and directional wells in composite salt layers. Background technique [0002] Salt-gypsum layer is a formation with salt or gypsum as the main component. It is a formation that is often drilled in the drilling process. It causes many complicated downhole situations and is extremely harmful to drilling engineering. It has always been the focus of domestic and foreign drilling circles. one of the problems. The composite salt layer contains salt rock, gypsum and mudstone at the same time, with many interbeds, large lithology changes and complex physical and chemical properties. It is the most common type of salt-gypsum layer and causes the most downhole accidents. Drilling fluid workers in my country have carried out a lot of research work on dr...

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Problems solved by technology

The creep characteristics of salt rock require a sufficiently high drilling fluid density to support the borehole wall (the density can reach 2.0g / cm 3 above) to prevent the shrinkage of the well diameter, which requires the drilling fluid to have a good sealing effect on the well wall and improve the pressure bearing capacity of the formation, so as to ensure that the high-density drilling fluid will not fracture the formation and cause leakage; at the same time, the drilling fluid under high-density conditions In addition, the gypsum in the formation absorbs water and expands, and the hydration of mudstone and gypsum mudstone can lead to wellbore instability; while the development of micro-fractures in some salt-gypsum layers provides drilling fluid loss channels, a large number of The entry of drilling fluid or filtrate into the formation exacerbates the above-mentioned rock dissolution and hydration problems, causing serious wellbore instability

③Drilling fluid lubricity problem

Existing relatively mature inorganic salt or organic salt saturated / undersaturated brine drilling fluids have been successfully applied in composite salt layers, but the overall application effect is not ideal, and there is a problem that the rheology of the drilling fluid is difficult to control under high-density conditions , irregular borehole diameter, poor wellbore stability, worsening rheological properties of drilling fluid after contamination, and high drilling friction, etc., resulting in frequent downhole complex situations, resulting in long drilling cycle and high cost in complex salt layers

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