| With the development of global economy, the demand for oil is increasing and all countries in the world are paying continuous efforts to develop oil and gas resource. With the appearance of new technology and the increase of drilling block, the requirement for drilling fluid is higher.In some special stratum, especially strong mud-making formation, clay invasion and mud making of drilling cuts can effect the rheological performance on condition that drilling fluid inhibit capability is not enough. In this situation, it is hard to open the pump and we can only maintain the performance by discharging the drilling fluid, dilution effect or adding some fresh drilling fluid. All the measures not only increase the material cost, but also increase the drilling time. The thick mud cake can be formed on the wall when the drilling fluid performance is bad, it also increase the filtration loss and cause wall instability.In order to meet the demand for drilling shale formations, drilling fluid system should has a certain inhibition.Mineral salts have been widely used to as inhibitor to prevent shale hydration, It can also bring some problem such as frequently bit bouncing, drilling hard trip, hole hard redressing and wall sticking owing to wall harden(hard hibition) caused by shale dehydration. Hydrated inorganic salts reduce swelling of the clay, it is also possible to cause flocculation of the clay, which will result in high fluid loss mud filtration and thixotropy. A further increase will reduce the salinity of the drilling fluid additives function. Another method of controlling the expansion of shale hydration in the drilling fluid is the use of the organic shale inhibitor molecules. Organic shale inhibitor molecules can be adsorbed on the clay surface.In order to meet the high requirements of drilling mud formations, we use a certain molecular weight polyamine-based agent, controlled by the addition of materials as well as inhibit the activity of cationic properties, synthesis, and developed a inhibition-balanced inhibitor material CPI.To solve the problem above, a great deal of research has been conducted including effect of different additive agents and an optimal solid free drilling fluid formula is found:seawater+0.5%PF-VIS-B+0.3%PLUS-B6+3%FLOCAT+3.0%CPI.heat-resisting property.Comprehensive performance of the system is evaluated indoor including temperature resistance performance, weighting performance, contamination resistance, inhibition performance and lubricating performance, the results showed that:(1) The recommended balanced inhibitive and stable rheology drilling fluid has a good heat-resisting and stability property under146℃by adding SPD. The drilling system can be used in a large temperature range between80to146℃.(2)Shale roller recovery rate is over97%.The system has a good clay inhibition performance and wellbore stability performance. It has a stable rheology under the condition of different substances contamination.(3) In case of shale and drilling cuts contamination, the system rheology property can keep stable and show a good contamination tolerance. Compared with other drilling fluid system, the rheology will not change in case of contamination and suitable for shale and strong mud-making formation.(4) In the system formation, we introduce an balanced inhibition method by using CPI. By changing and improving the system inhibitive way, we can prevent over inhibition with KCl, decrease hard trip accident and increase drilling rate.(5) The drilling system provides a good fluid-loss control capability to high permeability sandstone formation, due to the effect of FLOCAT and CMJ-H. It can be used in sandstone and shale formation.(6) PF-VIS-B is a viscosity control, shearing control and packet adsorption flow-adjusting material. It can get a better solid control result and improve sand-carrying capability, which can reduce the trend of large displacement horizontal and directional wells cuttings bed to improve hole cleaning, increase drilling efficiency. |
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