Multisensor research technologies of oil horizontal Wells on fields of the republic of tatarstan

In the Republic of Tatarstan the development widely involves hard-to-recover reserves of hydrocarbons, confined to low-permeable, heterogeneous and dissected reservoirs. Improvement of recovery efficiency of such reserves largely depends on the operational control system based on information about the filtration and thermal properties of the oil reservoir. Issues, related to the interpretation of geological field information, lead to incorrect mathematical problems in terms of Hadamard. The numerical solution of such problems requires the development of special methods. A mathematical model of thermohydrodynamic processes occurring in the ‘horizontal well’ system is constructed in the paper. Based on this model and regularization methods of A.N. Tikhonov, a computational algorithm is proposed for interpreting the results of thermohydrodynamic studies of horizontal wells and layers. Curves of the temperature changes are taken as the initial information, taken simultaneously by several deep instruments installed at different parts of the horizontal part of the wellbore. This approach makes it possible to evaluate the filtration parameters of an inhomogeneous reservoir and to construct an inflow profile along the trunk of a horizontal well.

Conducting and processing the results of thermohydrodynamic studies in the development of fields with hard-to-recover hydrocarbon reserves, as a rule, involve significant difficulties.These include: the mechanization of the producing wells stock, that makes it difficult to deliver deep measuring instruments to the bottom of wells; low rates, leading to low information content of debitometric studies; thermodynamic processes accompanied by small temperature changes; a long duration of hydrodynamic studies hindering the use of classical methods of interpreting pressure recovery curves.
Measurements of temperature and pressure in the trunk of a horizontal well based on multi-sensor technology (Farkhullin et al., 2003;Khairullin et al., 2006) provide quite complete information on the thermohydrodynamic processes occurring in the reservoir and the trunk.The change in temperature in the trunk of a horizontal well is an integral indicator of heat and mass transfer processes occurring both in the well itself and in the reservoir.
We will assume that the trunk of the horizontal well is parallel to the roof and the base of the reservoir; fluid movement in the trunk is one-dimensional.The process of pressure distribution in the trunk is quasistationary; the inflow of fluid to the trunk at the start of the well is radial.Under these assumptions, the laws of conservation of mass, momentum, and energy, it follows that (Vasilyev, Voevodin, 1968;Charnyi, 1975): , 0 <x≤ L, (2) , and boundary conditions , 0 <t ≤ t exp , ( 7) Here, p 1 =p 1 (x), T 1 =T 1 (x, t) is the pressure and temperature in the trunk of a horizontal well, p 2 =p 2 (x, r, t), T 2 =T 2 (x, r, t) is the pressure and temperature in the reservoir, p k -reservoir pressure, T k .-reservoirtemperature, q -horizontal well production rate, Strunk surface of a horizontal well, r c -trunk radius, R k -external boundary radius, β * -reservoir elasticity, v(x) -fluid velocity in the trunk of a horizontal well, ρ -fluid density, ε -Joule-Thomson coefficient, ψ -coefficient of hydraulic resistance, α m -coefficient of heat transfer of horizontal well trunk, C p -the specific heat of fluid, w -filtration rate, L -the length of the horizontal well trunk, t exp -operating time of the well.
The method of solving the boundary task ( 1)-( 8) is based on the conjugation of the external (reservoir) and internal (trunk of a horizontal well) tasks.The system (1)-( 8) is solved numerically by the method of finite differences.The filtration area is covered by a nonuniform grid, which thickens to the well.The resulting non-linear system of difference equations is solved iteratively.
The model task with data corresponding to the real deposits of the Republic of Tatarstan explores the thermohydrodynamic processes occurring in the "reservoir -horizontal well" system.
A simulated oil reservoir is considered, which is developed by a horizontal well.The horizontal well is put into operation with a constant recovery of liquid from the reservoir.Initial data: It is assumed that the permeability of the reservoir is a piecewise constant function.In each zone of the reservoir homogeneity, a deep instrument is located (Fig. 1).The following variants of zones of the reservoir heterogeneity are considered: In the trunk of a horizontal well, liquid comes from zones of heterogeneity of the oil reservoir with different temperatures due to the Joule-Thomson effect (Fig. 1).The change in temperature in the trunk of a horizontal well is due to the calorimetric effect.
The results of numerical calculations showed that for a homogeneous oil reservoir, the temperature along the trunk is constant and increases with time.The fluid velocity along the horizontal well trunk changes linearly.Figures 2-3 show the calculation results of the change in temperature and flow velocity for variants 1,2 at time = 120 h.The temperature (Fig. 2), the flow velocity (Figure 3) in the trunk of a horizontal well changes nonlinearly.The intensity of the fluid inflow to the trunk of a horizontal well (Figu.4-5) has a discontinuity at the point corresponding to the boundary of the reservoir homogeneity zones in terms of permeability.The distribution of temperature, flow velocity along the horizontal well trunk and the intensity of the fluid inflow to the horizontal well trunk depend on the permeability values and the size of the uniformity zones.
A distinctive feature of the inverse tasks of oil and gas hydromechanics, associated with the study of mathematical models of real filtration processes in oil reservoirs, is that the nature of additional information is determined by the capabilities of the field experiment.On the basis of the proposed mathematical model and regularization methods of A.N. Tikhonov, a computational algorithm is proposed for interpreting the results of thermohydrodynamic studies of horizontal wells.The results of measurements of the temperature change during the start-up period of the well at different sections of the horizontal well trunk are used as initial information.The locations of the deep measuring equipment are determined on the basis of geophysical studies of the well.In works (Farkhullin et al., 2003;Khairullin et al., 2006), a technology for performing thermohydrodynamic studies of a horizontal well with the help of several deep autonomous instruments is described.
Let us assume that in the locations of deep measuring instruments in the trunk of a horizontal well with coordinates x i , , the curves of temperature changes are taken: , 0 <t ≤ t exp . (9) The inverse coefficient task is formulated as follows: determine the permeability coefficient k=k(x,r), when the thermohydrodynamic processes in the oil reservoir and the horizontal well trunk are described by equations ( 1)-( 8).As the initial information, the measured values of temperature by deep autonomous devices are used.
An estimate of the permeability coefficient is sought in the class of piecewise constant functions k(x,r) = k n , (x,r)∈V n , , where V n , -homogeneity areas (Fig. 1).An approximate solution of the inverse coefficient task (1)-( 9) is sought from minimizing the root-meansquare deviation between the observed and calculated quantities: Where φ n (t) -the observed values of the temperature, T 1,n (t) -the calculated temperature values obtained from numerical solution of equations ( 1)-( 8), research of the horizontal well no 18326 (Nazimov, 2007).The well is located in the deposit No. 665 of the Romashkino field of the Republic of Tatarstan.The well has a 313 m open horizontal section in the Dankovo-Lebedyanskian horizon in the interval from 1475 to 1788 m.In 2004, deep thermohydrodynamic studies based on multi-sensor technologies were carried out in the well.Figure 6 shows the locations of the instruments.After the end of the underground repair, the well was put into operation with a flow rate of 7.8 m 3 /day.
The proposed computational algorithm is used to From the results obtained, it follows that the locations of instruments No. 1721, 1726 have a low permeability -in these sections the inflow to the trunk of a horizontal well is the smallest (Fig. 9).Geophysical  Estimates of conductivity in the locations of instruments Nos.1885 and 1879, obtained from the curves of temperature and pressure change are in good agreement.In interpreting the results of hydrodynamic studies, the skin effect was not taken into account, and therefore there is a discrepancy between the conductivity estimates in the locations of instruments No. 1721, 1726.Interpretation of curves of temperature variation µ k ( µ m 2 /mPa•s) 1.04 10 -3 2.13 10 -4 1.93 10 -4 1.07 10 -3 Interpretation of curves of pressure variation µ k ( µ m 2 / mPa•s) 3,42•10 -3 4,46•10 -3 3,63•10 -3 6,34•10 -3

Fig. 9 .
Fig. 8. Velocity distribution along the well trunk The results of the studies carried out by JSC Permneftegeofizika in mid-2006 with the LATERAL-2005 technological complex showed that in the areas where these instruments are located, a low inflow to the horizontal well trunk is observed.

Table .
Horizontal well No. 18326.Estimates of the filtration parameters