pH is a value representing the hydrogen ion concentration in liquid and it is used to indicate acidity or alkalinity of drilling mud. The pH is presented in a numerical value (0-14), which means an inverse measurement of hydrogen concentration in the fluid.
The pH formula is listed below;
pH = -log10[H]
Where: H is the hydrogen ion concentration in mol.
According to the pH formula, the more hydrogen atoms present, the more acidity of substance is but the pH valve decreases. Generally speaking, a pH of 7 means neutral. Fluids with a pH above 7 are considered as being alkaline. On the other hand, the fluids with pH below 7 are defined as being acidic.
In the drilling mud, there are three main chemical components involved in Alkalinity of drilling fluid, which are bicarbonate ions (HCO3–), hydroxyl ions (OH–), and carbonate ions (CO3-2). The Alkalinity means ions that will reduce the acidity. Continue reading
Solid content is a fraction of the total solid in drilling mud, and it always increases while drilling ahead because of drilling solid (cuttings), mud chemical additives and weighting material. Solid content refers to soluble and insoluble solid content in the drilling fluid system.
There are three types of solid contents as listed below;
– Soluble material such as salt
– Insoluble high gravity solid (HGS) such as weighting agents (barite, calcium carbonate, hematite, etc.)
– Insoluble low gravity solid (LGS) or drilled solid such as solids particles from cuttings
Mud filter cake is a layer formed by solid particles in drilling mud against porous zones due to differential pressure between hydrostatic pressure and formation pressure. For the drilling operation, it is preferred to have a filter cake that is impermeable and thin. Practically, the filter cake from API or HTHP fluid loss test should be less than or equal to 1/16 inch. If drilling fluid is not in a good shape, which results in a thick filter cake in the wellbore, it will lead to a stuck pipe situation and high torque/drag.
Mud Filter Cake from HTHP Fluid Loss Test (http://oilfieldpix.com/photo/679/Mud-filter-cake.html)
Fluid loss is one of important drilling fluid properties and two type of fluid loss are API and HTHP fluid loss. This article will explain about both of them and effect on the drilling operation.
API Fluid Loss Test
API Fluid Loss Test (low-pressure, low-temperature filtration test) is a test used to measure a filtration of mud with ambient temperature and 100 psi differential pressure. The API fluid loss testing equipment is shown below (Figure 1).
Figure 1 – API Fluid Loss Test Kit
How will the drilling mud be tested?
- Place a filter
- Add the sample into the testing chamber
- Place the chamber in the testing kit
- Apply 100 psi pressure
- Record volume for 30 minutes; at the end of the test the volume of filtrate will be recorded.
- Record thickness of filter cake
This is a simple example to demonstrate how to determine quantity of material required in a simple mixing system. Let’s learn from the example below.
The objective is to build mud which has a weight of 11.0 ppg with 1,000 bbl.
The mud recipe is shown below;
- 30 ppb bentonite
- 5 ppb CMC polymer
- 5 ppb caustic soda (NaOH)
- 25 ppb Na2CO3
- Weighting Material is barite.
The following are important data of water and chemical used for this calculation.
Base fluid = fresh water
Specific gravity of water = 1
Specific gravity of barite = 4.2
Specific gravity of bentonite = 2.4
Specific gravity of CMC polymer = 2.4
Fresh water weight = 8.34 ppg
NaOH and Na3CO3 have negligible volume because it is dissolvable.
What is quantity of material required to meet the mud specification?
What is the final volume? Continue reading