Geology. Geophysics. Drilling
PROMISING PERSPECTIVES OF OIL RE-EXPLORATION IN PALEOCENE SEDIMENTS OF BLAGODARNENSKAYA STRUCTURE IN STAVROPOL REGION
Stavropol Region is one of the oldest petroleum producing regions of the country. To date, much of its fields are depleted and prospects for the discovery of large hydrocarbon deposits have been exhausted. At the same time, there is still the possibility of opening small and medium-sized deposits localized in the source rock formations.
In the middle of the last century, similar deposits have been identified within Prikumsk-Tyulenevskiy (Praskoveyskoe, Achikulakskoye, Ozek-Suat and a number of other fields) and Chernolesskiy (Zhuravskoye, Vorobyevskoye) tectonic elements. However, these findings were largely spontaneous due to lack of approved and unified approach to the petrophysical evaluation of dedicated reservoirs from well logs. At the same time the experience of shale reservoirs studies, as well as the results of its implementation to evaluation of deposits of Zhuravsky-Vorobyevsky petroleum accumulation zone, allows to revise existing well log materials for deep wells of explorational and depleted structures, and to identify promising intervals for further re-exploration and testing.
In this work, Paleocene sediments of Blagodarnenskaya explorational structure of the Stavropol Region were studied. Despite the approval of the oil bearing of these deposits within the Prikumsk-Tyulenevskiy tectonic element and the positive signs of hydrocarbon saturation from initial well logs data, its evaluation and testing within Blagodarnenskaya structure dedicated to the North-Stavropol tectonic element, were not conducted. However, the results of well logs analysis performed by us with the use of interpretation technique approved on shale reservoirs of Zhuravsky-Vorobyevsky petroleum accumulation zone, as well as the core tests indicate the presence of oil-saturated reservoirs in the Paleocene sediments of Blagodarnenskaya structure.
The sum of the obtained results and confirmation of the oil saturation of Paleocene sediments on the other structures allows us to propose promising perspectives of re-exploration of the Paleocene deposits within Blagodarnenskaya structure. The presence of a large number of abandoned deep exploration wells suitable for the re-entry allows performing re-exploration by means of the existing wells fund without drilling a new one, what would significantly reduce costs and ensure the profitability of the operation in the event of success.
The results of investigations of the two samples of reagents carboxymethyl starch (KMC) and one sample of carboxymethylcellulose sodium technical grade CMC-9/N, the production of LLP “Cellulose Ethers” (Vladimir) for mining and geological, technical and technological conditions of the November oil and gas region of Western Siberia.
The first batch of CMC did not meet the quality performance indicators TU 6-55-221-1396-95, namely the nature of the dissolution. The kinematic viscosity of a 1% aqueous solution of the sample in the CMC received the order before production batch. Consequently KMC also differs from all test samples before KMC to influence the rheological, mechanical and structural properties of drilling fluids, the number of additives in muds. Recommended additives in this mud sample KMC should be increased by 1% or more.
Another sample corresponds to the KVM presented quality indicators for TU 6-55-221-1396-95 and refers to the high viscosity grades. This part can be used as structurant in formulations of drilling mud during drilling for conductor in an amount of 0.2-0.3%.
Experimental test CMC 9 / N corresponds to the data presented by advertising and a brand of low viscosity CMC. This grade CMC 9 / N can be used as a structurant in a composition of bentonite fluids while drilling a conductor in an amount of 0.3% or more, and drilling a main wellbore production tubing in an amount of not less than 0.5%.
Studied the influence of environmentally friendly lubricant additive SRGN (VNIIBT, Moscow) basic and special properties of bentonite suspensions and drilling natural polimergranita drilling fluids oil and gas region of Western Siberia. Given information about physical-chemical properties of the reagent. The results of the test reagent on the solubility in some environments. Presents experiments on the detection of the level of spanelement clay dispersion systems depending on the concentration of the lubricant additive. In these ranges of concentrations of reagents enough studied the stickiness of clay crusts created from artificial and natural solutions.
The above reagent has lubricating properties, however, not in all cases possible to use the reagent without antifoam. The active foaming of the solution occurs only when adding reagent SRGN in an artificially prepared bentonite slurry, adding in the drilling fluid accumulated in the well bore while drilling the well, the foaming does not occur. Technically acceptable concentration of the reagent is in the range of 0.5 to 3.0 % (vol.).
Sample reagent SRGN not adversely affect the basic properties of clay and polymer-clay solution. It is important that the rate of filtration of the solution and the coefficient of stickiness of the filter cake are reduced by a significant amount already, adding a reagent in the amount of more than 0.5%.
Presented the reagent can be applied in the fields of Western Siberia. You should pick up in the composition of the compatible agent and to provide the necessary level of frost resistance of the lubricant additive SRGN, because it’s important in winter to the far North.
For the prevention of complications and emergency situations in the process of drilling wells it is necessary to pay due attention to the processing of drilling fluid lubricant additives. Experience with various domestic and foreign lubricating additives in Western Siberia is described, for example, in scientific papers [1-30]. In recent years, there are constantly new types of reagents and their modifications that need to be adapted to the conditions of drilling wells in specific geological conditions. When selecting reagents, a preference for environmentally friendly lubricant additives.
The results of studies of sodium carboxymethyl cellulose (Na-CMC) produced ZSM “Polymer” (Ekaterinburg), pilot batch production of the “Polymer” (Ekaterinburg) and industrial samples technical CMC brand 83/600 of production of JSC Plant of construction materials “Polymer” (Ekaterinburg).
All presented samples of the CMC refers to a group of high-viscosity reactants, which are actively infilled artificial and natural clay solutions. The first chemicals suitable for clay mortars used in drilling wells in the November oil and gas region under the conductor in the amount of 0.3-0.5%. The second reagent is recommended for drilling fluids used in well drilling under the conductor in an amount of 0.3-0.5%, while drilling under the production casing – 0.5-0.7% 0.05% NTF to reduce the structural and rheological properties. The third reagent is recommended for drilling fluids used in well drilling under the conductor in an amount up to about 0.5-0.6%, and for dissection of productive layers in an amount of 0.5-0.7% from thinning additive of 0.05% of NTF.
In artificial suspensions of bentonite and natural clay solutions with the addition of the reagent CMC temperature control has different influence on the rheological and structural-mechanical properties. Filtration performance and the thickness of the clay cover in the treated natural clay solutions is always lower than in the bentonite suspensions. A significant influence on the manifestation of the properties of the reagent CMC in the washing liquid having the composition and quality of the clay component of the drilling mud.
In domestic and foreign practice invert emulsion drilling fluids (EDI) get more widespread in well drilling and completion, which ensure successful well steering in complex geological conditions, where using of water-based muds do not allow incident-free drilling. The reason is, first of all, that the hydrocarbon phase is neutral respectively to passable rocks, including salts and clays.
Increasing of EDI using is defined by constantly increasing quality demands while opening of reservoirs which is the most important stage in the cycle of well construction. One of the particular difficulty is the opening of reservoirs with long horizontal wells, since the natural reservoir properties of the rocks decrease with depth increasing. Using water-based muds in such conditions leads to the deterioration of the permeability of bottomhole formation zone and the need for a large amount of work on the flow stimulation.
Primarily, IDE is used for opening of productive layers with the aim of preserving their reservoir properties, represented by salt deposits, and swelling clays and other rocks, losing stability when in contact with water-based solutions
This article discusses a number of shortcomings of EDI, such as high aggressiveness of dispersion medium, and a significant decrease in rheological properties associated with increasing temperature as well as methods for solving these problems.