How to Measure K+ Concentration in Mud?

Mud properties are things that every day I’m dealing with. my mudschool instructor once said, controlling it is like a juggling, when any properties go off-spec, then we need to get them back while controlling others to be in acceptable range. For example, when The YP (yield point) goes up either because of contamination or increasing of solid, it affects to the increasing of ECD (equivalent circulating density). Higher ECD, obviously, going to be dangerous for drilling operation as there’s a limit for pressure in wellbore. The YP must be reduced ’till the allowable range. It can be done by dilution, addition of defflocculant, reduction solid content, etc. If first option is taken, mud weight will be goes down. See? 🙂 ,

So far I work with Water Base Mud with KCl-Polymer system. The standard mud properties that I always measure are mud weight, funnel viscosity, PV (plastic viscosity), YP (yield Point), gels strength, API fluid loss, pH, alkalinity (Pm, Pf, mf), hardness (total, Ca specific), K+, MBT, sand content, and solid content. It takes about 45 minutes to complete all the procedure. It’s so chemistry. A basic chemistry actually.

The comparison of cuttings evidence in Shale Shaker. an adequate concentration of K+ looks much nicer and smooth (left), otherwise it got sticky cuttings (right)

K+ concentration is important parameter and being one of the main concerns when drilling a shale or clay formation. The K+ will be going down in mud out from the well, as some of them is stick in shale/clay formation to inhibit water invasion into it (prevent swelling). One of the cuttings evidence when the K+ is depleted is sticky and often stuck in shaker, when we have adequate K+ concentration, it looks much nicer and easily coming out like smooth with no sticking each other. The practical field test to measure K+ concentration in is by hand crank centrifuge. Following are the procedure:

Equipment:

the apparatus needed and the precipitate formed when it’s already cranked

1. Clinical centrifuge tubes: Pyrex, Kolmer-type (Corning #8360) only, 10 mL
2.  Centrifuge: horizontal-swing rotor head, manual or electric, 1800 rpm
3. Standard sodium perchlorate solution: 150 g in 100 mL distilled water3
4. Standard potassium chloride solution: 14.0 g dry KCl dissolved in distilled water and made up to 100 mL in a volumetric flask, 0.5 mL of standard KCl solution made up to 7.0 mL with H2O = 1% KCl solution

Preparing Standard Curve for Potassium Chloride

curve of precipitate

1. Prepare standards over the range of 1% to 8% KCl by adding the appropriate number of milliliters of standard potassium chloride solution (0.5 mL per 1% KCl) to centrifuge tubes and diluting to the 7.0 mL mark with distilled water.
2. Add 3.0 mL of sodium perchlorate solution to each tube.
3. Centrifuge4 for one minute and read precipitate volume immediately.
4. Plot milliliters of precipitate versus percent potassium chloride, using rectangular graph paper as shown in picture

Field Procedure

1. Measure 7.0 mL of APl filtrate into the centrifuge tube.
2.  Add 3.0 mL of sodium perchlorate solution to the tube. If potassium is present, precipitation occurs immediately.5
3. Centrifuge for one minute and read precipitate volume immediately.
4. Determine potassium chloride concentration by comparing precipitate volume measured with the standard curve for potassium chloride.
5. Immediately dispose of precipitate by rinsing from tube into bucket of water. Dump water in a remote area of drilling site so that the precipitate can disperse and decompose.

High Potassium Chloride Concentrations

The accuracy of the method is dependent upon measuring potassium concentrations between approximately 2% and 8% KCl. If the filtrate potassium concentration is much less than 2% KCl, the method becomes inapplicable. If the filtrate potassium concentration is greater than 7% KCl, dilution may be accomplished as follows:

1. Pipette 2.0, 3.0, or 4.0 mL of filtrate into the centrifuge tube and dilute with water to the 7.0 mL mark.
2. Correct results by multiplying % KCl by 7, divided by volume of filtrate used (2.0, 3.0, or 4.0 mL).

DON’tT USE IT. I found a curve for standard KCl solution and its formula in any rig. Actually, the curve is specific for every KCl as some packaging has different purity

Practically in the field, we measure with simple way with not really accurate result. Sometime I feel that’s not true. The procedure must be applied whatever it takes. So first, I have to make a standard solution, then make a chart, then bla..bla..bla. Quite time consuming 🙄 . When there’s a lot of time available.

Table for K+ concentration in different amount of precipitate

Well, one of my senior really did a great job in it. He does really brilliant. Here’s the things: we can used a table to know how much K+ concentration directly from the amount of precipitate. Let say, when I got 2.6 mL amount of precipitate, so I got 2.5 ml = 60.664 plus 0.1 mL = 2406 or 63070, we wrote it thousands commonly, so it was reported around 63000 mg/L. how’s that? Smart, right? 🙂