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Drilling, mining

FEATURES OF DRY MIXTURES FOR OIL AND GAS WELLS CEMENTING

The article describes a relatively new and promising direction – the usage of dry cement mixtures in oil and gas wells construction. The key to the success of the cementing quality and is correctly selected for the specific conditions of tampon mixture. Until recently, the grouting mixture was made to cook directly in the field using mobile workshops, equipped, usually pneumatic supply and mixing of the components and then loads of ready mix in cement. In recent years, the method of producing cement mixtures in the factory, where the mixture is prepared in areas with better infrastructure and then delivered to the field, well established itself. The authors substantiate the possibility of dry cement mixtures at various downhole conditions using a mixture of appropriate additives, and describe the effect of additives on the parameters of the cement slurry. Despite a number of features that distinguish grouting mixture of traditional building, in their formulations, mainly used similar additives: water retention, pla-stifitsiruyuschie, accelerators, retarders, fiber, polymer powders. Widespread additives with special properties (materials, to prevent fluid loss, weights, oblegchiteli) due to the specific nature of downhole conditions. Special conditions of application of cement slurries and imply specific requirements applicable to the oil and gas industry in the traditional additives for dry construction mixtures. So, for polymer powders backfill material should consist of polymers with short chains and to be thermally stable when used at elevated temperatures. Many of the used oil and gas additives have complex effects on the backfill solution. Competent selection of additives, based on data about the geotechnical conditions at a specific field, provide qualitative dry grouting mixture, the use of which is the key to successful cementing operations.

ESTIMATION OF TIME EFFECT ON SIZE OF WASHOUT OF LITHIFIED SHALE

Stability of wellbore is one of the main factors affecting the well construction process on every stage – staring from drilling and end run and cement casing. Instability of open hole lead to such problems as significant washouts, increase in torque and drag, stuck pipe, low quality of logging and cement job.

Lithified shale deposits create about 70% of all problems related to instability of open hole. Currently the description of the root causes of the instability of shale as well as different methods and methodic to solve this problem could be found in different open sources. Most of them reference to the time dependent wellbore instability in shale formations, meaning that longer hope keeps open – higher probability that shale will lose the stability.

As it was proven in several studies the shale stability problem is related mainly to penetration of drilling fluid into laminations / fractures (between bedding planes and through the microfractures of shale) causing the mechanical failure and thus the loading of the well with cavings. It was noticed that amount of cavings increase over the time and has been suggested that filtrate of a drilling fluid continue penetrating into the formation and bigger volume of a rock is affected.

The objective of this paper is to review the effect of time on the size of washouts in shale deposits and estimate the boundary values when shale loses the stability.

ON THE SOFTWARE OPTIMIZATION PROCESS OF DEEPENING WELLS

It is shown that to increase the stability of the drill string in order to use software control, it is necessary to introduce a correction in a consistent framework for reducing the order asterisms control object. Correcting such links should be the differentiator. Along with this, shows the block diagram of software-based control optimal control of deepening wells.

It is proved that input the PID automatic regulator control of penetration allows you to convert an unstable object control (DC) in a stable that is in the process of governance to eliminate failure in self-oscillating mode. At the same time, as a measuring device used dual-channel power meter and drive speed, made by the method of dynamic measurements. The functional diagram of the automatic control system optimal deepening wells.

It is shown that control of the process and its optimization is possible by stabilizing the control loop for inclusion in the feedback loop PID controller, and also that the optimal control of the drilling process is to manage the dynamic pounce torque on the drive shaft a drilling installation.

Effect of formation strength of lithified deposits on stability of wellbore

Wellbore stability is one of the major problems while drilling oil and gas wells. Shale, in turn, makes up about 75% of drilled formations, and over 70% of the borehole problems are related to shale instability [1] costing the industry, accordingly to conservative estimates, $700 million annually [5]. As it was proven in several studies [6] the shale stability problem is related mainly to penetration of drilling fluid into laminations / fractures (between bedding planes and through the microfractures of shale) causing the mechanical failure and thus the loading of the well with cavings. In other words, the fluid invasion clearly weakens the shale making the shale stability very sensitive to the drilling fluid design. If the drilling fluid weight is too low, the risk of wellbore collapse increases. If drilling fluid weight is too high, drilling fluid invasion into these fractures and subsequent shale weakening makes the wellbore prone to instability. As a way to prevent or minimize the loss of wellbore stability the drilling fluid system includes proper bridging agents together with right drilling practices were proposed. At the same time it was noticed that shale in the same interval and formation reacts differently to drilling process. Some of them showing significant washouts and signs of instability and other stay stable and have in gauge hole. It has been suggested that stability of shale formations affected also by formation strength. And there are boundary values after which formations collapse and significant washouts occur. To prove this assumption the analysis of formation strength of shale was performed. The objective of this paper is to show the impact of formation strength to the stability of the wellbore in shale formations. The paper also provides the relation between thickness of layers and depth of washouts, and the boundary values of formation strength when shale loses the stability.

Development of sodium silicate-based inorganic water shut-off composition for low-permeability heterogeneous reservoirs

The article is devoted to development of low-viscosity water shut-off composition based on sodium silicate aqueous solution with an adjustable mechanism of gelation, the application of which will improve the efficiency of remedial cementing operations in conditions of heterogeneous low-permeability terrigenous reservoirs of Western Siberia. Evaluation criteria for determination of optimal concentrations of chemicals were as follows: gelation time, yield stress and gel plastic strength. Based on the results of the research it was found that sodium silicate aqueous solutions are capable to gel when interacting with chrome alum; it was also determined that changing the sodium silicate – chrome alum ratio makes it possible to adjust strength characteristics and gelation time of the composition proposed. The effectiveness of application of the water shut-off composition developed is confirmed by the results of low-permeability terrigenous core sample filtration studies with water shutoff treatment simulation in heterogeneous layered formation. It has been established that the proposed composition has selective insulating properties and to a greater extent reduces permeability of saturated intervals. After treatment with water shut-off composition it is recommended to inject a 15%- aqueous sodium hydroxide solution in order to restore permeability in oil-saturated interlayers with no destruction of the insulating shield in water-saturated reservoir compartments. Application of water shut-off composition during injection well treatment will make it possible to reduce amount of produced water and involve the previously non-draining oil stocks in the development; in addition, the alkali slug injection will restore filtration properties of oil-saturated intervals and increase oil relative permeability due to the effect of alkaline water flooding.