For many years gilsonite borehole stabilizer and other asphalt-type products have been used as additives to aid stabilization in water-based drilling fluids and to evaluate their effectiveness, it is well documented that these additives can reduce pore collapse in water-sensitive, molting-shale structures. The causes of borehole instability are many. The causes of instability can be mechanical, chemical or physical in nature. Mechanical problems include borehole erosion due to high annular velocity, adverse hydraulic stress due to high annular pressure, hole collapse due to high smear and impact pressure due to excessive wall cake, stress loss due to drill wire movement. Problems with physical instability include shale rock crumbling and blasting due to subnormal pressure or overpressure relationships of hydrostatic and formation pressures.
Fractures and sliding along faces under hard, brittle rock and collapse of fractured rock on divergent holes are also physical problems when drilling hard rock. This problem also arises in undisturbed holes when drilled in pressurized shales. Borehole instability problems are often referred to as molting, swelling, spalling or pressurized shale, mud rounds, mud rings, and many other descriptive names. There are many solutions to this problem. The use of additives to prevent or partially prevent soil swelling is well documented. Adjustment of hydraulic conditions is another solution to reduce mechanical changes. Knowing and controlling the pore pressure of problem formations is often used. This article discusses the use of gilsonite and asphalt-type additives to reduce physical changes and, to some extent, chemical changes. It has been difficult to assess the effectiveness of gilsonite and other asphalt products in the laboratory, as most testing processes are carried out at ambient temperature and low-pressure A procedure has been used to evaluate various water, base and oil based mud systems for rock stability Many manufacturers of asphalt-type products and many oil companies try to compare the effectiveness of these products with other products that reduce chemical change shell problems These tests are conducted in the laboratory at ambient temperature and low pressures.
Because gilsonite and some asphalt-type products require temperature and pressure to be effective, the results of these tests are skewed toward additives that control shale problems through chemical reactions. Chevron's Drilling Technology Center's Drilling Mud Services division began looking for "apples-to-apples"-based products of gilsonite and gilsonite and asphalt types Evaluated products using existing testing procedures at ambient temperatures: such as triaxial testing for shale stability, lubrication evaluation and effects on filtration control. The results of the first series of tests indicated that more in-depth evaluation is needed where the additives begin to work well. Several new test procedures have been devised, including the use of modified high temperature and high-pressure liquid loss cells, as well as downhole simulation cells. The results of these tests indicate that these procedures can be used effectively to evaluate and distinguish gilsonite and asphalt-type products. In addition, the use of a downhole simulation cell allows the user to distinguish or rank the effectiveness of gilsonite and asphalt additives with additives that reduce borehole instability due to chemical containment problems.
theory As mentioned earlier, gilsonite is classified as asphaltite and is a relatively pure hydrocarbon with no significant number of mineral impurities Gilsonite used for oilfield purposes is mined in the area around Bonanza, Utah, has a specific gravity of 1.05 with a melting point of 370°F to 400°F, although a material with a lower softening point (330°F) is available. It has a low acid number, zero iodine number and is soluble in aromatic and aliphatic hydrocarbons. It is processed and grounded where 80% goes through 80 grid bands, holds about 5% in 100 grid bands, and 30% in 200 grid bands Gilsonite asphalt materials have been used for many years to stabilize runoff shales to reduce borehole erosion. It was proposed that material added to the mud system before problematic shale was encountered, as bit formation entered rock pore spaces, microfractures, and bed faces released into gilsonite pores, fractures, and bed surfaces via a plastic flow mechanism reducing or reducing filtration and total mud attack. Schwartner found that gilsonite was superior to blown asphalt additives because of a higher softening point and fewer impurities In addition, it has been proposed to fabricate a thin film by plating gilsonite on the borehole wall. But blown asphalts containing sulfonates penetrate deeper into fractures because of their high solubility and do not "plate" as well as insoluble materials It was difficult to duplicate the effectiveness of gilsonite as a stabilizer for boreholes in the laboratory, as was seen in the field. Several companies have published data on ambient temperatures and pressures. Many of the tests mentioned are or are designed for additives that stabilize shale or soil by partial containment or encapsulation.
Because extrusion of gilsonite and insoluble fly asphalts requires both temperature and pressure, these additives do not compare favorably with environmental, low-pressure tests. Tests must be designed with higher temperatures and pressures to effectively evaluate gilsonite and asphalt content. The HTHP liquid loss cell/baria core test provided data that can be used to distinguish differences between different gilsonite and asphalt additive maintaining the same pressure to distinguish between gilsonite with different softening points at which different temperatures tested They can do it. Measurements of penetration depth, any penetration or full attack or flow can be used to select a suitable gilsonite Many more tests have been conducted by our company. This indicates that the product is not ductile enough to penetrate the matrix or that there is not enough temperature and pressure to remove the additive Deeper penetration shows that the temperature and pressure are sufficient for removal to occur. Full invasion or flow through the core indicates that the additive has been treated for dispersibility and solubility and not clogged or inter-matrix filter cake formation. Inspection of the core cross section showed the formation of a thin inter-matrix filter cake with gilsonite products. Penetration was limited to less than 2 mm.