DILUTE DRILLING FLUID

Dilution refers to the process of adding a liquid phase to a drilling fluid to decrease the drilled-solids concentration. Dilution is used in several ways. If no solids-control equipment is used or if the equipment is used ineffectively, dilution may be the principal method of keeping drilled solids to a reasonably low level. This is an expensive solution to the problem. For example, to decrease drilled solids by 50% requires that 50% of the system be discarded and replaced with clean drilling fluid. Usually dilution is used after processing by solids-removal equipment to dilute drilled solids remaining in the drilling fluid. Dilution may be added as a clean drilling fluid or as the liquid phase of a drilling fluid with the other necessary drilling fluid ingredients, usually through a chemical barrel and a mud hopper. In this discussion, dilution will refer specifically to the clean drilling fluid necessary to decrease drilled-solids concentration. Clean drilling fluid is the liquid phase with all necessary additives such as barite, polymers, clay, etc.

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THE PROCEDURE OF MECHANICAL SEPARATION EQUIPMENT USED TO PROCESS DRILLING FLUIDS

PROCEDURE

1.Collecting Data for the Capture Analysis

A sample set of each of the three process streams should be obtained, sealed, and labeled for identification. The size of each sample should be 50–100 ml. For each set, the time between catching each of the samples should be as brief as possible.

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ACCURACY REQUIRED FOR SPECIFIC GRAVITY OF SOLIDS

Determination of drilled solids in a drilling fluid depends on an accurate determination of the mud weight, the total solids in the drilling fluid, and the density of the drilling-fluid ingredients. For example, with a freshwater 11-ppg drilling fluid containing 2.6 SG low-gravity solids and 4.2 SG barite, a change in only 1%vol measured solids concentration makes a 2%vol change in calculated low-gravity solids. In Table 12.4, for an 11-ppg drilling fluid, a 13%vol solids concentration would indicate 6%vol, and a 12%vol solids concentration would indicate 4%vol.

Table 12.4
Solids Concentration in an 11-ppg Drilling Fluid

VLG(vol%) Vs(vol%) MW(ppg)
8 14 11
6 13 11
4 12 11
2 11 11

 

VLG=volume of low-gravity solids; Vs=volume of total suspended solids;
MW=mud weight.