TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA laboratory experiment has been conducted to study the behavior of water coning under a horizontal wellbore having a stinger inserted. A large Hele-Shaw cell was used to perform the experiment. The length of the stinger employed, oil viscosity, and initial thickness of oil column were varied to investigate their effects on the optimal length of the stinger.Results obtained show that systems without stinger yield better early recovery performance. Installing a stinger flattens the cone of water and reduces the rate of increase in water cut, leading to an improved recovery significantly. It is found here that the optimal stinger length is about 0.3 of the length of the horizontal wellbore section, regardless of the initial thickness of oil column and water/oil mobility ratio.

Formation damage around a horizontal wellbore has been a long-standing problem. The damage zone is expected to be a cone-like shape, extending from the heel end to the toe. This situation leads to a difficulty in studying the inflow performance. In fact, previous studies assumed clean and homogeneous formations and ignored any skin factor in predicting pressure drops along a horizontal wellbore, critical rate, and water breakthrough time. The present study is focused on investigating influx and flowing pressure distribution along a horizontal wellbore in the presence of non-uniform formation damage. The relevance with the inflow performance is also discussed. Modified wellbore hydraulics correlations coupled with a reservoir inflow equation are used to accommodate this effort. Calculations are performed for different skin distribution, damage severity quality, and wellbore diameters. Results obtained show that non-uniform skin causes reduced influx rate toward the heel end. The undamaged well reveals an opposite trend as expected. For a given total production rate, the influx rate at some portions of the wellbore increases as the formation damage gets heavier, as well as for smaller wellbore diameter, resulting in greater pressure drops. Thus, the presence of non-uniform skin promotes an increase in pressure gradients within the wellbore. The changes in pressure losses are more sensitive to the level of damage severity in smaller wellbore diameter. Such a study has not been previously reported in the literature. Overall, this investigation improves our knowledge to better understand flow behavior in a horizontal wellbore. The paper presents information to be considered in predicting the inflow performance and also provides a guide for deciding or optimizing a horizontal well completion strategy. Introduction Invasion of mud filtrate into a productive zone during drilling the well has been a long-standing problem. The residing mud filtrate and also the mud particulates can cause damage to the zone by reducing the permeability around the wellbore. This in turn results in higher pressure losses in the vicinity of the wellbore and thus reduces productivity of the well. Any damage around wellbore is therefore never desired because formation damage is also costly. When one gets his well damaged then his company unfortunately has to spend a lot of money and time for damage removal in order to put the well back on its natural capacity. Drilling a horizontal well causes the productive zone being exposed to the drilling fluid for a quite long period. A portion of the wellbore, particularly nearby the heel end, has the longest exposure time and therefore has the greatest skin radius. In a sensitive formation, the damage can be so severe that the horizontal well is irreparable. In the case of conventional vertical wells, Hawkins1 presented a model and the related equation for estimating the skin factor that can be used for calculating flow efficiency of a vertical well. To model skin distribution along a horizontal wellbore, Frick and Economides2 have successfully made representatives of formation damage distribution for horizontal well in isotropic and anisotropic reservoirs and come up with an analytical expression for damage. Many studies have been conducted3–9 to evaluate the effects of formation damage on horizontal inflow performance. These studies, however, have mainly focused on the well productivity or flow efficiency. In a comparison with conventional vertical wells, a relatively high ratio of horizontal-to-vertical well productivity can result in serious production losses of the horizontal wells. Some other investigations10–16 have looked deeper at inflow mechanism along a horizontal wellbore, including aspects of wellbore hydraulics. The results in general show that wellbore pressure losses can be quite significant when production rate is considerably high and/or wellbore diameter is relatively small. Unfortunately, formation damage that frequently occurres in horizontal wells has been ignored in such investigations.

The use of multilateral well is becoming an emerging method to improve oilrecovery efficiently. A stacked multilateral well can produce fluids from twoor more separate productive zones. Unlike a commingled vertical well, inflow performance relationship (IPR) of a multilateral system is influenced by wellbore hydraulics of the horizontal boreholes. As a rock and fluid properties may vary considerably from one zone to another, construction of the composite IPR would become a necessity in an effort to evaluate and optimize the production performance. The purpose of the present study is to investigate the effect of pressure losses along the horizontal wellbores on inflow performance of a multilateral well system. A mathematical model is used here to calculate pressure losses within the weilbores and the productivity indices as well. A procedure to construct the composite IPR of a multilateral well and a method to predict the production decline are presented. A parametric study of wellbore hydraulics of a multilateral well system has been conducted. In general, results obtained show that increasing pressure losses in the lateral holes leads to the IPR curve shifting downward and reduced daily oil production. These demonstrate that production rate estimation for a given multilateral well would be too optimistic when pressure losses are omitted. No such work on stacked multilateral wells has been reported in the pertinent literature. Overall, this paper provides some information to better understand the application of multilateral well technology and to improve our knowledge of the importance of wellbore P. 245

TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractAlthough application of horizontal well technology is categorized as a relatively new and expensive but it has been proven more effective and efficient in producing oil. However, the production rate strategy to obtain optimal result has not been well developed due to the difficulties to identify the influence and interaction of forces related to fluid flow mechanisms in reservoir. Particularly for oil reservoir with bottom water drive, the movement of water-oil contact/interface in a reservoir is strongly affected by interaction of the acting forces, such as: viscous force, gravity force and capillary force.The main objective of this research is to study and investigate the influence of the forces interaction on production performance of the horizontal well producing oil from bottom water drive reservoir. For this purpose, a physical scaled model has been successfully constructed to simulate the prooduction performance. Scaling down and construction of the model are performed by using dimensional analysis.Results show that the interaction of the forces in the reservoir strongly affects the well production, in which the production performance increases as the ratio of gravity to viscous forces increases for all cases examined. Meanwhile, the changing of capillary force, which was believed by several researchers that it has no pronounced effect to the fluid flow mechanism in the reservoir, shows significant effect to the production performance of the well. The influence of reduced capillary forces in reservoir will enhance the well production performance. Consequently, in term of the ratio of gravity to capillary force, an increase in the ratio tends to improve the oil recovery.

llds paper waa s=lscted for presentation by an sPE Program Committee following rw'ew of information conkined in an absbacf submitkd by the author(s). Contenk of the paper, as presantsd, have not been reviewed by the Society of Petroleum Engineers and are subject tõ n by the author(s). The matarfal, as p-entsd, doss not nw=sarily refkcf any position of the Socfety of Petroleum Engineer'a, ifs offfcers, or members Papers preaent8d at SPE meetings am subject bJ publication m"ew by EdtirialCommittees of the -ety of -Ieum Engine=&~-tic reprodu~on, distribution, or storage of any part of this paper for commercial PUPSCS without the wnttan mnsent of the~i~of Petroleum Engineers is prohibikd PermMon to reproduce in print is reatdcted ba an absfrati of not more than-,~uafrations may not be qid. The abstract must contain conspicuous ackndedgment of where and by whom tie paper was presented Write Librarian, SPE, P 0 W.Richardson. TX 7=88S8. U S A. &x 01 -972-9S2-94S5. AbstractAmong multilateral well systems, that can be drilled using today's technology, more than t~w dml and q~d lateral wells have been successfully implemented in an oil field.l The advantage gained over single Iateral wells is an increased reservoir access per weIl drilIed. There are some investigations deaIing with inftow performance and economic evaluation of multilateral wells, excluding dual and quad Iaterals. Therefore, further reservoir engineering and eeonomic studies should be conducted to evaluate the potential of these dual and quad well 8ystems for improving the profitability of reservoirs. The objectives of the present work are to study the effect of reservoir characteristics on the production performance of a dual and a quad laterals and to evaluate the economic attractiveness when compared with a single lateral well. Based on the &fiormance prediction model used and the mnomic evaluation. results obtained show that the use of such multilateral wells would be economically more attractive for reservoirs with low-to-medium permeability. Also found, on the basis of the comparison made here, that the economic benefits are influenced as well by the magnitudes of reservoir anisompy, the lateral holes placement, and producing rate.Overall, from a reservoir management point of view, the results demonstrate the importance of adequate reservoir characterization and the production strategy in the applications.