To understand better the effect of interfacial tensions (1FT's) on gas/oil relative permeabilities, with particular emphasis on those effective in condensate reservoirs, an experimental procedure was developed and used with the highly volatile methane/propane system. The objective was to measure steady-state relative permeabilities as functions of 1FT. Thus the 1FT was varied from 0.03 to 0.82 dynes/cm [0.03 to 0.82 mN/m], corresponding to pressures near the critical at a constant temperature of 70 D F [21 DC].Individual relative permeability curves obtained as a function of gas saturation approach the 45 D [0.79-rad] diagonals for both gas and oil as the 1FT is lowered. This supports the expectation that relative permeability curves for both gas and oil become straight lines as the 1FT approaches zero. At the highest 1FT for which experiments were performed (0.82 dynes/cm [0.82 mN/m]), the relative permeability curves approached those obtained for a nitrogen/kerosene flood for which the 1FT is approximately 30 dynes/cm [30 mN/m].The most important conclusions derived from this work are that (I) the curvatures of the relative permeability curves diminish as the 1FT is reduced, (2) the irreducible gas and liquid saturations approach zero as the 1FT approaches zero, and (3) relative gas/oil permeabilities for gas-condensate reservoirs are altered from the normal relative permeabilities only at pressures, temperatures, and compositions close to the critical point.

Tar mats are extra heavy oil zones sandwiched between aquifers and adjoining oil columns. They isolate either partially or completely an oil reservoir from its aquifer. This results in a rapid pressure drop, a premature high gas-oil ratio and a low primary oil recovery; all of which point to some form of pressure maintenance early in a field's life. Eventhough tar mats represent considerable hydrocarbon reserves as they are rather common in the Middle East and Africa, it is their impact on oil recovery from adjoining oil columns which is of interest for the time being. Tar must be characterized to evaluate its mobility and ways of establishing contact between an oil column and its aquifer as well as to design an optimum water injection scheme. The present paper discusses a detailed chemical characterization of tar from a carbonate reservoir in Saudi Arabia. Thermal stability variation was evaluated by thermal gravimetry (TG), and differential thermal analysis (DTA). Elemental analysis of preserved and non preserved samples were carried out with a Carlo Erba 1106 elemental analyser. The sulfur content was also determined by two different ASTM methods. The presence of Nickel, Vanadium and Iron, the major metals usually found in hydrocarbons, was investigated by X-ray fluorescence (XRF) spectroscopy. The tar major hydrocarbon group components were separated and quantified by high performance liquid chromatography (HPLC). Experimental results showed variation, in tar properties, with depth and area within the same field. The carbon to hydrogen ratio increased systematically with a decrease in API gravity. The sulfur contents obtained with the Carlo Erba elemental analyser were in good agreement with those obtained by the general bomb method (ASTM D-129-64). The content of Hexane insolubles was relatively high at about 38 % by weight. The polar compounds ranged between 5 and 9 % by weight.

Saudi Arabian Well Log Analysis System (SARLOG) is a computerized open hole well log interpretation system developed locally for the Ministry of Petroleum and Minerals. This system consists of a total of forty subprograms. These subprograms will digitize and prepare data, perform chartbook environmental corrections and do perform chartbook environmental corrections and do level by level main calculations. Cross plotting subprograms are included for verification of log calibration, identification of lithology, differentiation of gas and oil and determination of all formation parameters. As the equations and methods used in well logging depend on lithology type, shaliness and available log combination, optional methods have been included in SARA to allow the log analysts to put his own judgement when it becomes required. Six shale indicators are used to approach a mere precise shale value, and seven water saturation methods are optional for shaly sandstones and complex carbonate lithologies. Introduction In the past few years, computers have become one of the most powerful tools for log analysts. Many oil companies and institutions have developed their own software and are still developing new methods in computer and well logging technology. Computers are capable of doing the most complex log analyses in a reasonable amount of time. The interactive communication and graphics capability of the computer, facilitates its utilization by a log analyst who has not had any previous computer experience. The SARIS (Saudi Arabian Log Analysis System) is a computerized well log analysis software system which is developed for the Ministry of Petroleum and Minerals by the University of Petroleum and Minerals Research Institute (UPMRI). This software is designed for open hole well log analysis and consists of various subprograms for performing comprehensive computations and elegant displays. The task of the system has been distributed into five main stages with each of the subprograms functioning as an element in one of the following stages:digitization and data preparation,chartbook environmental corrections,cross-plotting,main interpretation, andpresentation. The SABLOG has been developed to be applied to the interpretation of various log combinations, geologic settings and probable situations related to well logs which might be encountered in Saudi Arabia. The software was developed and applied on both the complex carbonate and shaly sandstone reservoirs. SABLOG is broken into sub-programs to provide more flexibility and the ability to apply to various data combinations. The system has been developed in RP basic language to run on the HP 9845C computer and was later translated to Fortran language to run on the IBM 370/158 system. The specifications and utilization of each version are explained in separate user's manuals. The SARLOG system has been developed by following the essentials of Schlumberger logs and the Schlumberger Log Interpretation Chartbook. HARDWARE The HP BASIC version of the SARLOG system was developed for use on the HP 9845C desktop computer system (with associated peripherals) presently at the UPM Research Institute (Fig. 1). presently at the UPM Research Institute (Fig. 1).

The application of enhanced oil recovery (EOR) for a Saudi Arabian carbonate reservoir was the subject of this study. Initial process screening revealed that miscible displacement was the only viable EOR process for recovering the relatively heavy oil (28 ° API). The use of separator gas, separator gas enriched with liquefied petroleum gas (LPG), pure LPG, CO2, and CO2 enriched with LPG as displacing fluids was explored. Some of the experimental results were presented in the 1987 Middle East Oil Technical Conference (see ref. 1). Further results obtained from a continuation of the study are described in this paper. The minimum miscible pressure of pure CO2 with oil was found to be higher than the reservoir pressure. CO2 enriched with 15 percent LPG gave optimal multiple-contact miscibility conditions. An unconventional apparatus consisting of a slim tube and a core holder joined in series was designed to study multiple-contact displacement. It was found to be very useful for investigating the effectiveness of enriched CO2 as a displacing fluid. The conclusions of this experimental study for the carbonate cores were:Oil displacement efficiencies by LPG and enriched CO2 were comparable, although the displacement mechanisms were different.The optimal size of LPG and enriched CO2 was 5 and 25 percent, respectively.Water alternating with gas (WAG) gave similar results when used in place of continuous CO2 as driving fluid.CO2 acted as an excellent buffer for separating the displacing fluid from the driving fluid.The amount of oil recovered by the miscible process was twice as much as that recovered by waterflooding. INTRODUCTION Several researchers have demonstrated that multiple-contact miscibility (MCM) tests require certain length or travel distance before the miscibility develops. Their reports2,3,4,5 showed that short cores could not be used in MCM displacement experiments to estimate the recovery from large scale systems. In this study, an improved linear model, called combined slim-tube coreflood apparatus, was employed to perform MCM enriched CO2 tests. This unconventional model consisting of a 41 foot (12.5 m) long slim-tube connected in series with a core holder, allows the miscible bank to develop in the slim-tube and then miscibly displace the crude out of a 12 inch (30.5 cm) composite core. Holm6 and Ehrlich et al7 have used similar experimental models for achieving the same purpose.

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