core analysis
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The penetration of drilling mud fluid into core samples can significantly impact the accuracy and reliability of laboratory analyses. Here are some effects that can result from drilling mud fluid contamination:
1. Alteration of Porosity and Permeability Measurements
Drilling mud can clog pore spaces in the core, leading to artificially low permeability and porosity readings. This affects the evaluation of the reservoir’s ability to store and transmit fluids.
2. Changes in Fluid Saturation
The introduction of mud can displace or mix with the natural reservoir fluids (oil, water, or gas) in the core. This distorts fluid saturation measurements, leading to incorrect assessments of hydrocarbon content and reserves.
3. Chemical Contamination
Drilling mud often contains various chemicals, which can react with the core materials. This can alter the mineralogy or chemical composition of the core, skewing results in tests like geochemical analysis or X-ray diffraction.
4. Inaccurate Wettability Studies
Wettability, or the ability of a fluid to spread on the surface of the rock, is crucial for determining fluid behavior in the reservoir. Drilling mud can change the rock’s surface properties, affecting wettability measurements and misrepresenting how oil, water, or gas would naturally flow in the reservoir.
5. Altered Mechanical Properties
Mud fluid infiltration can soften or chemically alter the core material, leading to inaccurate readings of mechanical properties such as compressive strength, affecting predictions for wellbore stability and reservoir behavior under stress.
6. Biased Formation Water Salinity
The salinity of formation water is important for resistivity logging and other calculations related to fluid content. Mud invasion can contaminate the core with foreign fluids, distorting salinity measurements and impacting resistivity and hydrocarbon saturation estimates.
7. Disturbance of Gas Content
For gas reservoirs, drilling mud can affect the gas content in the core, either by dissolving gases or preventing their natural release. This results in inaccurate estimates of gas reserves and production potential.
In summary, drilling mud contamination can compromise core analysis, leading to incorrect interpretations of reservoir characteristics, potentially affecting reservoir management decisions and overall project success.