Causes of oil and gas formation damage during drilling
Release time: 2015/10/26 Ai Yi NewsViews : 2152
During the drilling process, there are many reasons for the damage of the drilling fluid oil and gas layer. When drilling the oil and gas layer, under the action of positive pressure difference and capillary force, the solid phase of the drilling fluid enters the oil and gas layer, causing pore throat blockage, and its liquid phase entering Oil and gas layers interact with rocks and fluids in the oil and gas layers, disrupting the original balance of the oil and gas layers, thereby inducing potential damage to the oil and gas layers and causing the permeability to decrease. The reasons for the damage of drilling fluid oil and gas layers during drilling can be summarized as follows.
1. The dispersed phase particles in the drilling fluid block the oil and gas layer, and there are a variety of solid phase particles, such as bentonite, weighting agent, plugging agent, temporary plugging agent, insoluble matter of drill cuttings and treatment agent, and polymer fisheye. The solid phase particles in the drilling fluid that are smaller than the pore throat diameter or fracture width of the oil and gas layer are blocked by the pressure difference formed between the effective liquid column pressure of the drilling fluid and the pore pressure in the formation and cause blockage in the pore throat and fracture of the oil and gas layer. Layer damage. The severity of the damage increases with the increase of the solid phase content in the drilling fluid, especially the content of the bentonite which is very finely dispersed has the greatest effect. The degree of damage is related to the size of the solid phase particles, gradation and type of solid phase. The depth of solid phase particles intruding into the oil and gas layer deepens as the pressure difference increases.
2. Damage caused by incompatibility between drilling fluid filtrate and oil and gas reservoir fluids. Incompatibility between drilling fluid filtrate and oil and gas reservoir fluids can induce potential damage factors of oil and gas layers. Inorganic ions contained in inorganic salt precipitation filtrate interact with inorganic ions in formation water to form water-insoluble Salts, such as filtrates containing a large amount of carbonate and bicarbonate, form calcium carbonate precipitates when they encounter formation water with high calcium ions.
3． The damage caused by the change of the phase permeability, the filtrate of drilling fluid enters the oil and gas layer, changes the distribution of oil, gas and water in the area near the wall of the well, resulting in the decrease of oil phase permeability and increase of oil flow resistance. For the gas layer, the invasion of the liquid phase (oil or water) can adsorb on the surface of the reservoir seepage channel and reduce the cross-sectional area of the gas seepage, or even completely lose the gas seepage, resulting in "liquid phase traps".
4． Damage to the oil and gas layer caused by the drastic change in negative pressure difference. If the negative pressure difference is too large during mid-testing or drilling with negative pressure difference, it can induce the sensitivity of the oil and gas layer and cause sand and particle migration in the oil and gas layer. For fractured formations, excessive negative pressure differential may also cause fracture closure on the well wall surface, resulting in stress-sensitive damage. In addition, organic scale can be induced in crude oil components in the formation.