Research And Application Of The Shale Gas Well Oil Based Mud System

The total of the global shale gas resources is456.2trillion cubic meters, accounting for about half of the global unconventional gas resources. Shale gas development is an emerging energy industry, mainly concentrated in the United States, Canada and other developed countries. U.S. shale gas production reached210billion cubic meters in2011, accounting for about21%of U. S. natural gas production, China’s geological conditions is suitable for the formation and enrichment of shale gas. Although shale gas development is still in its infancy, but has great potential and good development prospect, and realistic strategy importance to increase domestic oil and gas support capabilities and enhance national security. Shale gas widely exists in organic-rich shale and mud shale, mainly in the form of adsorption and Free State, buried similar with coalbed methane, with self-generated and self-storage characteristics. Wind range and large area, typical low porosity and permeability, which determine the shale gas development is difficult and technically demanding. Currently, with great support of the country, the development of shale gas has been some progress, the development mode using horizontal wells.Oil-based mud has been study as early as the beginning of the20th century, the foreign has formed mature oil-based mud system, the study is late and still in the research, trial and perfection stage. Compared with the water-based drilling fluids, oil-based drilling fluid with anti-pollution ability, lubricity, strong inhibition, is conducive to maintaining wellbore stability, can maximize the protection of the reservoir, and oil-based drilling fluid and stable performance, easy maintenance, temperature resistance ability and great thermal stability. The use of oil-based mud can solve some problems which water-based mud can hardly resolve, especially in the piedmont structure, high density deep wells and shallow water extended reach wells. If the oil-based drilling fluids used in such strata, the overall complexity of the drilling process will reduce, drilling speed can greatly increase, and the integrated drilling costs will be reduced. Shortcomings of oil-based drilling fluid is mainly in high cost, bad for logging operation, serious impact to the environment and damage to the reservoir.Shale gas horizontal wells oil-based drilling fluid using water-in-oil emulsion drilling fluid, mainly for control mud shale collapse, reduce the friction drag during drilling progress, decrees the occurrence of the phenomenon of sticking, improve the drilling cycle, save integrated cost. The mechanism of this system is that the water present in the emulsion is more, the greater the chance of droplets aggregation and consolidation. Assumed that the drops of the same size, the small water content of the system is more stable, if the water content is the same the finer the water and the emulsion will be more stable, large water drops more easily than the small droplets coalescence, in addition to the size of the water droplets more uniform, The emulsion is more stable. Therefore, in order to make the water in oil emulsion, it is necessary to add enough emulsifier, so that the each polka circumference formed integral membrane. In order to obtain finer small droplets of uniform size, should an external force in the way of cutting is applied to the system through the mud gun or the stirring action of the centrifugal pump to achieve. Especially in the preparation of oil-based mud, as possible the height of the shearcut mud is important.The preparation of Shale gas horizontal wells oil-based mud adopts the method of double tank and signer tank. Horizontal shale gas wells oil-based mud system consists of diesel, high temperature emulsifier, anti-high-temperature wetting agent, saturated brine, the lipophilic organic soil, oxidized asphalt, lime and heavier material. Shale gas horizontal wells oil-based mud having a wide range of density0.84g/cm32.64g/cm3, excellent theology, the low fluid loss and the filtrate is the oil rather than water, which is the main reason for oil-based mud can effectively protect the reservoir in the shale formation and complex formation with strong water sensitively and easy to collapse. The electrical stability of the electrical stability (ES) test measured value is higher than ordinary oil-based mud. Shale gas horizontal wells oil-base mud is easy for field maintenance and treatment. Absolute rheological property such as plastic viscosity and yield value, and the shear force is difficult to determine, it can be influenced by temperature, pressure, solid-phase particles, the ratio of oil, brine concentration, emulsion stability, etc. In large borehole and high-angle wells require a higher yield value and shear plastic viscosity as low as possible, so that can often get the maximum penetration rate, as much as possible to control the solid phase in the mud, and the solid phase the smaller and more good. Lime can be used to control the alkalinity of the mud, the key factors determining the success of shale gas horizontal wells in oil-base mud. Often measured residual quantity of lime mud system, so that the values within the range of1.5%to2.5%, which can ensure an emulsifier to obtain the best performance, improve the high temperature stability of the system, to prevent the occurrence of ionizing. An excess of lime will promote the water wetting effect, an excess of lime is harmful, the need to reverse wetting agent, the lime consumption in the new system and instability is very rapid, the system is stable when consumption is very slow, which daily Determination of alkalinity, and maintained in an appropriate range. Oil-water ratio is the ratio between the oil and water components of the emulsion, which means that the percentage of the total liquid component. The ratio of oil to water depends on the initial viscosity of the system and HTHP water loss. The activity values of CaC12brine is0.4to1.0, the activity values of fresh water is1.0, the minimum activity value of NaCl brine is0.75, according to strata need to select the appropriate brine. Note that CaC12brine and NaCl brine activity is not additively.Waste drilling mud is pollutant produced during the drilling progress, Containing mineral oil, phenol compounds and heavy metals complex multiphase system the leaching fluid has a higher toxicity, long-term accumulation can cause serious damage vegetation, pollution of soil and water, and even can endanger the survival of mankind. Through the combination of ultrasound and chemical d\emulsif ication method to recover oil and water in waste mud, then separating muddy water two-phase effective by coagulation treatment.There will be some high-viscosity mud left in the wellbore and causing potential damage in the use of oil-based mud drilling. Oil-based mud wetting formation near the borehole wall, resulting in decreased permeability, which is oil-based mud invasion into the near-wellbore damage caused. A surfactant for cleaning the wellbore cake and oil-based mud, to raise the level of well is produced.Overall, shale gas horizontal wells oil-based mud is adapted to the country’s energy development strategy; adapt to the shale formations, to shorten the drilling cycle, increase productivity, play the role of the limitless.