. The purpose of this research is to study the area near the bottom of the hydrocarbon well, which is usually affected by drilling and dev elopment operations, and to find a modern method that improves the transfer of fluid from the reservoir to the well. The area near the wellbore of an oil and gas format ion is a very active and unstable zone. Field studies have shown that during the process of drill ing the first well into the pay zone, a new area of disturbed permeability and porosity forms a round the wellbore. This disturbed area is called the skin zone and is characterized by differ ent properties. The skin zone can also form during the completion processes of hydrocarbon well s. In terms of well test processing for any hydrocarbo n well, the term "skin effect" should be understood as the effect of changes in the lower we llbore zone (i.e., changes in rock properties, changes in formation fluid, formation structure, ge ologic section, etc.) on bottom wellbore pressure. This indicates a change in the permeabili ty of the bottom zone of the borehole during drilling and development. In this paper, a new computational method is propos ed in which the investigation of hydrocarbon well condition can be performed in two ways. The first way represents replacing the true radius of the wellbore (rw) with an effect ive radius (rwe). Under this condition, the skin factor term reflects only the effect of change s in the bottom wellbore zone. The second way is that the skin factor indicates not only the amount of change in the bottom wellbore zone, but also the effect of hydrodynamic imperfect ion of the hydrocarbon well performance during production, while maintaining the value of t he well radius. After evaluating these parameters, it is possible to conclude the effectiv eness of the implemented measures in the bottom wellbore zone of the formation. At the same time, the value of the skin factor after the performed works regarding the impact on the bottom zone can determine the positive or negative impact on the operation of the hydrocarbon well. Keywords .Skin effect, Bottomhole zone, Hydrocarbon well con dition, Wellbore radius, Hydrodynamic imperfection. 1. Introduction The There is no industry in which minerals are not extracted from the rock without drilling a well. These are oil, gas, water, metals dissolved in acid , and other elements. The method of drilling a well is very cost-effective and is widely used in mining an d commercial production [1-3]. The rock structure, rock pressure, synclines and anticlines, and minera l composition of the rock largely affect the proces s of hydrocarbon accumulation in a porous medium. The increase in rock pressure also affects the flow process of liquid and gas [4,5]. Hydrocarbons can accumulate in various rocks. Accor ding to their structure and characters, these rocks may be sandstone, dolomite, and limestone. Th e rocks sometimes differ in their granulometric or 50 Technium Vol. 3, Issue 4 pp.50-56 (2021) ISSN: 2668-778X www.techniumscience.com mechanical composition [6-8]. The reservoir propert ies of rocks also affect the process of oil accumulation. Thus, the normal type of reservoirs i ncludes carbonate rocks, the grains of which consist largely of shells, grain fragments and ooli tes. The cement of sandstone is very diverse (marl, calcareous, clay, siliceous, ferruginous and so on) [9-11]. The cementing material may be both primary, deposited with the sand grains and chemica lly deposited as a result of the diagenetic process between and around the grains, and secondary, depos ited from aqueous solutions that have penetrated the rock after deposition. Note that as the cement content increases, the rock may gradually changes t o a chemogenic rock. This process may degrade the res ervoir properties of the rock and gradually transform it into unproductive rock, creating a ski n zone in the bottom zone of the production well [12-14]. The nature of the structure and the size of the roc k cavities have a great influence on the reservoir properties of the rocks and the amount of hydrocarb on accumulation. Rock structure and voids (cavities) are classified as large, small and subca pillary. Hydrocarbons generally accumulate in capillaries, i.e. small cavities [15, 16]. Pressure affects the structure of the rock and the degree to which it is saturated with hydrocarbons. However, the resulting pressure (called hydrostatic reservoir pressure) has specific differences from the pressure generated by the rock (geostatic press ure). Hence, it is necessary to consider two groups of hydrocarbon accumulations [17-19]: (a) under normal reservoir pressure and (b) under abnormal reservoir pressure. However, during drilling or completion of hydrocarb on wells, additional resistance occurs in the bottom wellbore zone. The appearance of a new zone partially reduces the permeability of this zone. To solve this problem, we consider the simplest cas e when the entire reservoir can be divided into two sharply defined zones based on permeability, rock s tructure, porosity, etc. The coaxial well is intend ed to serve as a boundary between formation zones with different physical properties. There is an abrupt change in rock properties between the wellbore and the target zone. Note that in real conditions, the deterioration of the wellbore zone can be caused by the influence of low-grade clay mud when drilling a productive formation and developing a wellbore, w ashing the bottom with various fluids (water, acid, steam), clogging the pores of the formation a nd so on [20, 21]. The following very useful conclusions follow from t his: Disturbing of the hydrodynamic perfection of the production well and disturbing the near-bottom zone of the well do not prevent the determination of reservoir permeability throughout the well's dra inage area. However, the wellbore bottom disturbance and the hydrodynamic perfection of the well have a strong influence on the magnitude of downhole pressure drop [22, 23]. Since this downhol e pressure changes as a function of given wellbore flow rate, this affects the value of the c oefficient of hydrocarbon well productivity. Note that if the hydrocarbon well has a disturbance in the bottom-hole zone, the size of that zone wil l differ from the size of the formation. Authors of works [24, 25] introduced the concept of «skin effect». The English word "skin" literally means "outer layer", "shell". The addition of this parameter reflects the main idea of these authors. This parameter quantitatively characterizes the ski n effect of the lower zone of the borehole, which i s briefly called the skin factor index. Based on the above, it was necessary in this invest igation to find and improve a new calculation method for the production specifications for this a rea. 51 Technium Vol. 3, Issue 4 pp.50-56 (2021) ISSN: 2668-778X www.techniumscience.com 2. Methods of research Based on the approaches used to study hydrocarbon w ell conditions, a new calculation method was derived and performed. In the first approach, the t rue wellbore radius (rw) is replaced by the effecti ve radius rwe. In the second approach, the skin factor term reflects only the effect of changes in the lo wer wellbore zone. In the second approach, the value of the true wellbore radius was retained and the skin factor indicates not only the amount of change in t he lower wellbore zone but also the effect of hydrodynamic imperfection of hydrocarbon well perfo rmance during production. 3. Results and discussions It is known that the general equation - the law of flow - can be represented as:  =  .  (1) Where d eff is the effective diameter of the particles composi ng the porous medium, Sl is the dimensionless coefficient (Slichter number), V is t he velocity of the fluid flow, µ is the fluid visco sity ,dp/dr is the pressure gradient [26]. The effective particle diameter d eff can be calculated by:  =∑ ∑ (2) Where ni is the number of i th fraction, d i is the average diameter of the i fractions, determi ned by the formula: = ´+ ´´ (3) ´+ ´´ - Arithmetic mean of the extreme diameters The dimensionless coefficient (Slichter number), SI , is a value that depends not only on the porosity but also on the structure of the pore space, which is determined by the shape of the particles and the degree of roughness of their surfaces [27-29]. We t hus solve this problem for a one-dimensional radial flow of an incompressible fluid. To do this, we take the cross-sectional area of the reservoir to be A=2πrh, where r is the formation radius, h is the formati on thickness:  = 2 ℎ  .  (4) According to the linear flow law, we obtain: " =#     $% (5) Where Q is the fluid flow rate . 52 Technium Vol. 3, Issue 4 pp.50-56 (2021) ISSN: 2668-778X www.techniumscience.com Figure 1. Diagram of the near-wellbore region of a heterogen eous formation: ∆P fm - Reservoir pressure drop during fluid flow into an ideal wellb ore (with natural Sl (fm ) of the reservoir); ∆P fm.s - Total reservoir pressure drop during fluid flow int o a real wellbore (considering the skin layer with Sl (s) of the formation); ∆P s - Pressure drop at the wellbore bottom in the skin layer as a result of formation degradation. Based on Fig. 1, which describes the skin and forma tion zones around the well, we assume the following boundary conditions using (1): &" =# $%  '(& (*) (*) * ' +& (,) (,)  * - (6) Where deff (s) and deff (fm) are the corresponding effective diameter of the ski n zone and formation; Sl(s) and Sl (fm) are the Slichter numbers for the skin zone and for mation, respectively; Pw - bottom-hole pressure; Pe- external pressure; rw and r e - the radius of the borehole and formation, respec tively; rs - the radius of the skin zone. Integrating (6) , we obtain: "− " /=# $%(  (*) *ln * '+  (, ) , ln  *- (7) By rearranging, adding and subtracting the value ln * ' we get: "− " /=# $%  (, ) , ( (, ) ,  (*) *ln * '+ ln  *+ 23 * '− 23 * '- (8) "− " /=# $%  (, ) , (ln * '4 (,) ,  (*) *− 16 + ln  '- (9) By introducing the concept of skin factor: 53 Technium Vol. 3, Issue 4 pp.50-56 (2021) ISSN: 2668-778X www.techniumscience.com 7 = 23 * '4 (, ) , (*) *− 16 (10) In the final form, we then obtain: "− " /=# $%  (, ) , 87 + ln  '9 (11) From this formula, the value of the volumetric flui d flow rate can be obtained: : =$%  (, ) , µ(<  = =') (12) With these formulas, it is possible to assess the i nfluence of the skin factor on the pressure drop in the well bottom and the fluid flow rate. Numerous obser vations have shown that the skin effect assumes values smaller than S = - 6 in practice [30- 32]. W ith this value of the skin factor, a theoretically conceivable extreme case is considered, namely,  (, ) ,  (*) *= 0 (13) Field observations showed that this value of skin f actor was reached after hydraulic fracturing, but only on the basis of the calculations performed can a positive effect of hydraulic fracturing be concluded. In processing of numerous field studies, it was found that the value of the skin effect was very often large and positive. This indicates that the properties of the bottom wellbore zone deterior ate during drilling or well development. The analysis s hows that after carrying out special works related to the effects on the bottom wellbore zone, the new va lues of skin effect were lower than the previous ones. 4. Conclusion Considering the above, it can be shown that the ski n effect provides an assessment of the condition of the lower wellbore zone depending on various parame ters such as the structure of the pore space, the shape of the particles and the degree of roughness of their surfaces. These parameters must be taken into account when planning measures to improve the operation of a production well. The change in the value of the skin factor can be u sed to assess the success of the work carried out i n the lower borehole zone. This method of calculation makes it possible to jud ge the imperfection of wells in two ways. First, replace the true well radius with the effective rad ius. In this case, the value of the skin factor ref lects only the effect of changes in the zone of the well bottom. The second method is that the skin factor indicates not only the amount of change in the well bottom, but also the effect of the hydrodynamic imperfectio n of the production well during production, while preserving the value of the well radius.