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Oil Exploration and Production Wastes Initiative Project Methodolo <br />B. Drilling wastes <br />Points of Generation <br />Drilling for oil or natural gas resources generates drilling wastes. The estimated <br />total volume of drilling wastes generated in California during 1995 was 1,826,401 <br />barrels (API, 2000). These wastes consist mainly of formation materials <br />displaced during drilling and coated with drilling fluid. Soil and rock cuttings are <br />lifted to the surface by the fluid circulated through the drilling pipe and collected <br />into a nearby earthen pit, called drilling pit (see Figures 4 and 5). <br />Figure 4: Drilling Pit Showing Drilling Waste <br />Figure 5: Drilling Waste Aggregated with <br />Cement <br />The composition of the drilling wastes reflects the characteristics of the formation <br />being drilled, and the composition of the drilling fluid utilized. Drilling waste often <br />appears as sludge, with an aqueous layer floating on the surface. The <br />composition of the drilling fluid itself might vary, depending on the circumstances <br />of drilling. Typically a mixture of water and clay, drilling fluids may contain other <br />additives. A common additive is barite, a weighting agent, used to improve the <br />viscosity of the fluid and its ability to counterbalance the formation pressure and <br />to float soil material to the surface. Oil-based and synthetic fluids are used in <br />special circumstances, such as drilling to great depth or through high-pressure <br />formations. <br />Note: The drilling waste sampled for this project consisted of drilling pit contents <br />aggregated with cement. The drilling fluid used was water-based, with barite <br />used as a weighting agent. <br />Statewide Compliance Division May 2002 <br />-12- <br />