The objective of this study is to analyze the performance of non-conventional wells drilled in Hassi-Messaoud field, Algeria. A new technique "Direct Synthesis" developed by Dr. D. Tiab1,2 is used for the pressure transient analysis. It permits the determination of permeability tensor as well as the effective length of the horizontal well. Hence, and for the first time, the permeability tensor (Kx, Ky, Kz), and the vertical permeability anisotropy (Kv/Kh) were obtained. The results of the interpretations lead to a verity of information and correlations. Sensitivity studies allow the optimization of future horizontal drilling plannings. The comparison between the performances of slanted, horizontal, and multilateral wells shows that slanted wells, regarding the low risk, are the most appropriate for Hassi-Messaoud field. From the spatial distribution of permeabilities, Kx, Ky, Kz, important conclusions are illustrated regarding the geological model of the field. Horizontal wells are not only beneficial for improving productivity but also for the tremendous amount of information they provide. Form this study several recommendations are issued regarding the well spacing taking into account different geological models. Introduction Hassi-Messaoud field has four (04) reservoirs (R3, R2, Ra, and Ri). The Ra is the principal reservoir within 100m of average thickness; it is subdivided in five (05) layers or drains (D1, ID, D2, D3 and D4). The cutout of Ra is made in many zones that are limitted by the sectors of low characteristics. Historically, the produced hydrocarbons during the last four decades represent less than the half of mobile hydrocarbon in place. To reach the best recovery in Hassi-Messaoud oil field, two points should be realized:Perfect knowledge of reservoir architucture, andOptimal reservoir management and development. For the efficient investigation of petrophysical parameters and their spatial distribution, The reservoir is characterized by newly geostatistical methods. As a result, the structure of four units (R2, Lower Thick Level (LTL), D3-D4 and Riso) and the organization of petrophysical parameters in bands of high to average permeabilities, oriented in North-Est/South-West direction, are established. However, the development of sectors of low petrophysical chracteristics is conceivable only by the use of non-conventional techniques such as horizontal and deviated wells or by modifying oldest vertical wells to short or medium radii. It is important to summon up that previously in Hassi-Messaoud field, the scope of anisotropy (kv/kh) and the permeability tensor in space (kx, ky, kz) have never been measured. However, the present synthesis, based on field results of transient pressure response analysis performed on non-conventional wells, is well investigated for vertical and horizontal anisotropies evaluation. Analyses and Results In this work, the first step consists on analyzing pressure response by the following computer softwares, Saphir, Interpret II, and Welltest-PED using non-linear regressions as well as specialized plots. Knowing that these softwares present many limitations such as:Restrictive hypotheses in analytical methods.No means for result control, andShortage in output parameters for reservoir characterization in their globality.

This paper presents a part of a reservoir engineering study initiated in 1978 to evaluate secondary recovery projects by water-injection in so producing areas of the Algerian HASSI MESSAOUD giant producing areas of the Algerian HASSI MESSAOUD giant oil field. Paper mainly deals with the first part of the study : an in-depth description of the sandstone reservoir anatomy. Based on a concept of individualized sedimentary units, the description characterizes and classifies these units. It uses a systematic treatment of such as numerical filtering. The resulting picture of the reservoir, is an organization of good sand bodies distributed among a poor sandstone medium, into which are dispersed discontinuous shale breaks. Good sand bodies and shale breaks were characterized by their densities on the vertical, and by the frequency of their occurrence with depth. Permeability of the good sand bodies was found to be related to their density. When numerous, good sand bodies are individually more permeable than when they are scarce. The inferences of such a description on flow parameters, such as the effective horizontal and parameters, such as the effective horizontal and vertical permeability, and the effective critical gas saturation were extensively studied. Results were a better understanding of reservoir behaviour and a more rigorous simulation of dynamical phenomena. Thanks to this method, history matching was easily completed, thus saving time for further studies. Introduction The selection of data for reservoir simulation is generally a difficult task, specially in heterogeneous formations. Modern reservoir simulators are proved to be reliable on mathematical and physical proved to be reliable on mathematical and physical basis. Therefore the quality of the results depends on the quality of the data. Not only on the quality of each data by itself, but also on the imaginative concept which presides at their gathering and assembling into a model. Many unsuccessful attempts of predicting reservoir behaviour with numerical simulators predicting reservoir behaviour with numerical simulators were due to the lack of geological perspective, the necessity of which has been emphasize in the recent literature. When data assembling comes to a "cells filling", history matching is often difficult, tedious, and the resulting picture of the reservoir poorly reliable. poorly reliable. This paper tries to summarize studies which were performed on a producing area of HASSI MESSA field in Algeria. Main objective was the appraisal of the various possible drive mechanisms. Such a objective could only be achieved by the use of mathematical simulations. It was therefore decided, prior to the use of simulators to devote a large prior to the use of simulators to devote a large part of the effort to the reservoir description. part of the effort to the reservoir description. Results obtained from the simulations proved that such an effort was worthwhile. HISTORY SUMMARY Located in the Northern part of the Algerian Sahara desert (Figure 1), HASSI MESSAOUD field was discovered in 1956. Producing formation is a Cambrian sandstone encountered at 3 100 meters subsea. With oil in place over 2 000 × 10(6) m3, HASSI MESSAOUD is among the giant oil fields of the world. The oil is light - 45 degrees API. Original pressure is 473 bars. Production started in 1959, and after a few years, it appears that the whole field could be divided into relatively independant producing areas (Figure 1). Geologically and dynamically these areas are not completely separated from their neighbours, but the fluid exchanges are in most cases highly restricted by low permeabilities on the borders generally due to faults, in addition to similar rythms of depletion. Until 1964 the production mechanism was only depletion above bubble-point. At that date a miscible gas injection started, firstly limited to a portion of area 13, but which now extends to several areas (2, 6, 9, 14, 15, 19, 20, 25). For other areas (4, 7, 11, 12, 16, 17) a water-injection program was scheduled. One of the main problems of water-injection was to evaluate the best starting date.