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  costing the industry, accordingly to conservative estimates, $700 million annually . 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. 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.
The article presents the results of laboratory studies of lubricating additives Flotoreagent oxal , tall oil (TM) MCHAS 30% MCHAS TM and DRC – 4mm in the compositions of bentonite slurry and natural mud Noyabrskiy oil and gas region of Western Siberia. Physico-chemical properties of the reagents and their solubility in organic and inorganic media to the foaming properties of clay dispersed systems. However, the results of experiments to assess the degree of influence on the main reagents listed (the density, rheological and structural and mechanical properties, the pH, the rate of filtration, the thickness of the mudcake) and special (stickiness mudcake) the properties of natural and synthetic muds both before and after incubation. Recommendations on the use of additives in lubricants and natural weighted drilling fluids in the oil fields of the November region. To achieve the necessary technological parameters of natural muds need concentration and oxalyl DRC – 4mm not less than 1%. They exhibit less negative side effects, in particular, foaming of a solution, stable in time have a consistency exhibit good lubricating properties. Different batches of chemical products DRC – 4mm somewhat different with different characteristics and properties. Nevertheless, the level of necessary technological properties of natural clay solution treated with the lubricating additives of the data corresponds to the wiring requirements for deep oil wells.
The drilling of the production section in the development wells in South Iraq could face numerous problems related to the partial or total losses, flow of sulphurous water, significant change in pore pressure along the wellbore, tight hole and caving among others. One of the main issues observed in several fields across South Iraq during well construction is the stability of in the production section of wellbore (especially in the shale formations). The instability of the open hole led to time consuming incidents related to an inability to run open hole logs to the wells total depth. Additional time has also been spent on wiper trips, reaming and backreaming, and on incidents related to hole pack off and stuck pipe. To solve the problem several steps were taken starting with the creation of a mechanical earth model which identified the main problematic formations presented by shale and the possible root causes of instability. This involved core characterization analysis including X-ray diffraction, cation exchange capacity and thin section analysis were performed to identify the structure of the shale. In addition the fracture development tests were performed on the samples of core and from this the main root causes of instability were identified. Based on the theoretical research and the laboratory tests new drilling fluid formulation together with best drilling practices were proposed that would allow the elimination of the problem due to the stability of the wellbore in the shale formations.
About possibility of using drill muds as a component of grouting mixture in construction of oil and gas wells
On the basis of laboratory researches found impact of addition dolomitesed drill cuttings in cement dough on the quality of the main technological properties of the cement stone. The place of formation of drill cuttings is oilfield «Kitaymsko-Blagodarovskoye» in Orenburg province. Defined: addition of dry drill cuttings in cement dough until 5% mass. practically doesn’t spoil specifications of cement stone. With increase content of drill cuttings in cement mixture practically all main technological properties are worsed and this mixture doesn’t meet the requirements of the GOST. Nevertheless, addition of dry drill cuttings in cement mixture from 5% to 15% mass., gives such backfill, which could be recommended for using by placing of cement plugs and liquidation drilling mud losses. In order to give assess of possibility of using developed cement-drill by drilling oil and gas well-dones it is necessary carry out experimental industrial tests in real conditions. As a «filler» used dolomitesed drill cuttings, as we have already done in laboratory experiments. Reasonable criterias for evaluating the success of experimental industrial tests in real conditions to believe are: technical possibility prepairing mixture directly on the territory of oil&gas field and regulated technological indicators assessment of the quality of tampon-process works. In case obtaining positive results of experimental industrial tests in real conditions, developed method may be recommended for wide implementation on existing productions. Using of cement-drill cuttings by building oil&gas well-dones will not only optimize price of one drilled meter, but else greatly reduce anthropogenic influence on environment.