Study On Percolation Theory And Appliction For Multi-Branched Horizontal Wells

In recent years, multi-branched horizontal well technology has developed rapidly in oil industry. The technology is a combination of multilateral branched well and horizontal well, with double advantages of two technologies, it will be a single horizontal well trajectory to be changed multiple level section in the spatial distribution, thus we can use a main wellbore to exploit multiple oil and gas layer, increases the drainable area and single well controlled reserves, improves the oil and gas production. At present, there are relatively more researches on the multi-branched horizontal well drilling, completion and production technology at home and abroad, while relatively few researches on its mechanism of seepage and production. This paper is divided into six chapters, respectively, studied the deliverability of multi-branched horizontal wells and its influencing factors, flow characteristics of branch wellbores, steady and unsteady seepage rules of multi-branched horizontal wells. Major achievements and understanding as follows:(1) Analysis of common multi-branched horizontal well productivity calculation analytical model, to study the factors that affect of deliverability, the results show that branch length, branch number, reservoir thickness and the well location have a great impact on the output. Among them, the branch length and branch number exist an optimal value; thin-layer oil reservoir with multi-branched horizontal well can increase production significantly; well is located in the central reservoir, horizontal well has the largest output; the total output of herringbone well in the branching angle of90°at maximum. Study on the influences of wellbore trajectory on horizontal well output, conclude that the strength of anisotropy determines its impact trends. Study on the optimization principles of horizontal segment length, that Dikken’s optimization principle underestimated the potential of reservoir development by horizontal wells, and puts forward the ultimate output optimization principle.(2) Study of horizontal wellbore pressure drop impacts on production, obtained the pressure distribution pattern when exists variable-mass flow in wellbore, analysis of the relationship between the frictional pressure drop, acceleration pressure drop, mixed pressure drop, total pressure drop and wellbore flow rate. The results show that wellbore total pressure drop from toe to heel increases gradually, radial inflow increases the total pressure drop, but reduces the frictional pressure drop; frictional pressure drop and wellbore flow rate into non-linear increase relationship, and its proportion in total pressure drop is the largest; as well as flow rate of wellbore heel increases, the increased proportion of acceleration pressure drop is greater than frictional pressure drop; the wellbore total pressure drop calculated by semi-analytic method is greater than the result which used average flow rate method, and more accurate; mixed pressure drop is mainly affected by axial velocity, radial velocity and inflow angle, increases with the increase of axial velocity and radial velocity, and with the inflow angle changes from small to big, radial inflow gradually by the maintenance of wellbore pressure change to cause pressure drop, when inflow angle of180°at maximum pressure drop.(3) Though the establishment of reservoir-wellbore steady seepage coupling model, research on the production characteristics of plane radial multi-branched horizontal well and herringbone multi-branched horizontal well. As for plane radial multi-branched horizontal well:the branch interference leads to production less than a single equal length horizontal well; branch length and branch angle have a great influence on production, we can adjust the branch length and branch angle in order to equal each branch well production, and form the equilibrium displacement; the flow rate from toe to heel is gradually increased, with heel reaches the maximum value, the radial inflow along production segment presents an asymmetric U-shaped distribution, the radial inflow closed to heel is obviously less than closed to toe, when the wellbore trajectory is bent, it is no longer a smooth curve, but with the wellbore trajectory change fluctuation.As for herringbone multi-branched horizontal well:the radial inflow along main wellbore is not a simple U-shaped distribution caused by the wellbore interference, but suddenly inflow decreases in the branch wellbore heel junction with the main wellbore. Herringbone well production mainly affected by the branch number, branch length, branch angle and branch configuration. The design should not be too many branches, there is more incremental production for increasing branch length than adding a new branch; greater production when branch length and branch angle are not equal, drilling a long branch wellbore nearby the main wellbore heel is more conducive to increase production; ipsilateral branch structure to contribute more to production, the production for branch wellbores which have a public convergence point is slightly larger than non-public convergence point, and the radial inflow of main wellbore at the convergence point decreased significantly; when the branch wellbore is located at the both ends of main wellbore and large distance, the main wellbore radial inflow is smaller.(4) Though the establishment of reservoir-wellbore unsteady seepage coupling model, studied the unsteady seepage rules of non-coplanar dual-lateral horizontal in the box-shaped closed reservoir; application of point source function method, Newman product principle, Laplace transform and its numerical inversion method, studied the transient pressure for multi-branched horizontal well, plotted the pressure and pressure derivative curves. The results show that:the potential distribution of different branch wellbores is basically the same, but the gravity leads to a great pressure difference between the various branches; with the increase of production time, the reservoir pressure and wellbore pressure are corresponding decline; difference from steady seepage, the radial inflow along branch wellbore is no longer a U-shaped distribution, in the initial stage of production, the inflow distribution of different branch wellbores changed slightly, remained basically unchanged, with the conduct of production, the inflow distribution of the branch wellbores changed significantly, near the wellbore heel the flow rate decreased, while near the wellbore toe the flow rate increased. In the early of unsteady seepage, due to the interference between branch wellbores has not yet formed, the pressure characteristics of different multi-branched horizontal wells are basically the same, but increase as time increases; in unsteady seepage advanced, pressure derivative values of different multi-lateral horizontal wells tend to N12. Comprehensive and systematic study on the seepage theory of multi-branched horizontal well and its application in reservoir engineering, has important theoretical and practical significance for efficient exploitation of reservoirs, this is just about the purport of the dissertation.