During the exploring, drilling, and workover of petroleum oil and natural gas, the borehole wall is easy to lose water, cause the change of well diameter and collapse of oil well, so that the project can not be carried out normally, even to give up halfway. Therefore, it requires adjusting the physical indexes of drilling mud according to geological conditions, well total depth, temperature, the thickness of different areas. And CMC is the best product to adjust these physical indexed, with the main effect:
1.1 Mud with CMC can form thin and firm filter cake with low permeability on the borehole wall. Prevent hydration of shale and the spreading of drillings. Reduce the collapse of the good wall.
1.2 Mud with CMC is a kind of high efficient fluid loss agent. With a lower dosage (0.3%-0.5%) can well control the fluid loss level, and won't cause poor influence on other performances of mud, such as too high viscosity or shearing force.
1.3 Mud with CMC is high temperature-resistant. Usually, it can be applied under 140℃ high-temperature environment. If use CMC with high substitution degree and high viscosity can be used under 150℃-170℃ high-temperature environment.
1.4 Mud with CMC is of salt-tolerance. The performances of CMC on salt-resistance are: keep reducing dehydrate under certain salt concentration, retain certain rheology effect, and have little change compared with that under freshwater environment. Can apply in clay free drilling fluid, and mud under the saltwater environment. Some are salt-resistant in drilling fluid with small rheology. Especially the salt-resistance CMC produced by Fortune Biotech, the change ratio of viscosity has increased above 1 under 4$ salt concentration and freshwater. That is, viscosity is almost no change in a high salt environment.
2.1 Improve the performance of filtration and mud cake quality. Increase anti-jamming ability.
CMC is a kind of good fluid loss additive. Apply in mud can raise liquid phase viscosity and seepage resistance of filter liquor, so control fluid loss at the lowest level.
The add of CMC can make mud cake compact, firm and smooth. Reduce the situation of logging tool sticking owing to the migration of drilling tools. Reduce resisting moment on rotating aluminum rod. Relief the suction phenomenon in the borehole.
CMC dosage in common mud is 0.2%-0.3%. API fluid loss can reduce greatly.
2.2 Improve the shale carrying effect. Increase the stability of oil slurry.
Owing to good thickening property, so even if bentonite content is lower, it can still retain the desired viscosity of carrying debris and suspending barite as long as adding adequate CMC.
2.3 Resist dispersion of clay. Prevent collapse.
The reduction of the fluid loss function of CMC can slow down the hydration speed of mud shale on the borehole wall. As well as covering function on the borehole rock of CMC long-chain, can strengthen the rock structure. Not easy to collapse and spalling.
The normal construction of cementing for good cementation is an important part to ensure good cementation quality. Spacer fluids with CMC have characteristics of reducing flow resistance and facilitating construction, etc..
During the operation of formation testing and workover, serious pollution to oil rock will arise if using hight solid mud. To eliminate the pollution is much harder. If only use clear water or brine as workover fluids, it may cause serious leakage. Even water blocking may form due to the water from filtration on the oil rock. Or result in a partial expansion of the mud in the oil rock, and permeability damages.
Apply CMC for workover fluids can successfully solve the above issues. Can use formulations according to the fluid loss level for low-pressure borehole or high-pressure borehole.
Low pressure layer: light fluid loss: clear water+0.5%-0.7% CMC. Common fluid floss: clear water+1.09%-1.2% CMC. Serious fluid loss: clear water+1.5% CMC.