Theoretical Study of Coning Toward Horizontal and Vertical Wells in Anisotropic Formations: Subcritical and Critical Rates

Abstract

Theoretical Study of Coning Toward Horizontal and Vertical Wells in Anisotropic Formations: Subcritical and Critical Rates I. Chaperon I. Chaperon Total-CFP Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Annual Technical Conference and Exhibition, New Orleans, Louisiana, October 1986. Paper Number: SPE-15377-MS https://doi.org/10.2118/15377-MS Published: October 05 1986 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Get Permissions Search Site Citation Chaperon, I. "Theoretical Study of Coning Toward Horizontal and Vertical Wells in Anisotropic Formations: Subcritical and Critical Rates." Paper presented at the SPE Annual Technical Conference and Exhibition, New Orleans, Louisiana, October 1986. doi: https://doi.org/10.2118/15377-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Annual Technical Conference and Exhibition Search Advanced Search AbstractStable cones created by a horizontal well drilled with maximum clearance from the unwanted fluid are studied (Muskat type approach, using pertinent viscous flow potential), yielding practical values for the critical rate potential), yielding practical values for the critical rate per unit length of a horizontal well, and for the critical per unit length of a horizontal well, and for the critical cone elevation, depending on both vertical and horizontal permeabilities, oil thickness, both fluid gravities, and oil viscosity. Critical rate weakly decreases when vertical permeability decreases.The same type of analysis is repeated for a vertical well completed over a very short interval (modelized as a point source) also with maximum clearance from the gas point source) also with maximum clearance from the gas cap or water table, yielding values of critical rate and cone height for the vertical well. In this case the critical rate slightly increases when vertical permeability decreases. permeability decreases. The outcome of a comparison between both types of wells shows that a critical cone comes closer to the horizontal well than to the vertical well. Also horizontal wells generally allow higher critical rates than vertical wells, however this advantage lessens with increased anisotropy. Very simple formulas are provided to evaluate what gain in critical rate may be obtained from a horizontal well.IntroductionThe use of horizontal wells to produce hydrocarbon reservoirs appears as a possible solution to some particular drainage problems such as isolated low particular drainage problems such as isolated low productivity layers, the will of restricting coning productivity layers, the will of restricting coning phenomena and maintaining monophasic production. Also phenomena and maintaining monophasic production. Also these may be a solution to environmental problems (highly deviated wells are enough, ending horizontal is not the key factor in this case). So far the best application of horizontal wells is the pilot development of a tight karstic formation with some high permeability fractures that a horizontal well is likely to intercept (which is statistically almost impossible for a vertical wells), containing highly viscous oil in presence of a bottom water drive.However, horizontal wells do not solve all problems, and even when one horizontal well produces twice more than a vertical one, is it worth the investment (and risk) as compared to two regular wells ? To answer this kind of question that a reservoir or production engineer is often faced with, it is necessary to study in details how oil flows towards a horizontal well as compared to a vertical well : changes in flow lines, influence of vertical and horizontal permeabilities, changes in viscous flow potential far from and close to the well. These detailed studies should provide simple formulas (and a guide to how and when to apply them) that anyone may use for evaluation purposes. Most reservoir engineering results of the french research group "FORHOR" have been gathered and presented in ref. 2, for practical use. Concerning coning, one ideal case only was published but cannot be applied as such.The scope of the present paper is to provide a simple and practical estimate of the critical rate to be expected from a horizontal well in realistic conditions (steady-state or pseudo-steady-state, anisotropic formation), and compare it to that of a vertical well to estimate a possible gain in rates. It concerns static stable cones or crests as illustrated by Fig. 1 but not diphasic production. Water cones (vertical wells) or crests (horizontal wells) follow the same equations as gas, except for the fact that they form below the wells instead of above. The descriptions hereafter concern oil flow in presence of a gas cap so as to avoid repetition of the reverse case of oil above water. Keywords: flow in porous media, upstream oil & gas, flow potential, anisotropy, reservoir, vertical well, viscous flow potential, permeability, unit length, cone Subjects: Reservoir Fluid Dynamics, Flow in porous media This content is only available via PDF. 1986. Society of Petroleum Engineers You can access this article if you purchase or spend a download.