Measurements of reservoir rock properties are a difficult task. These rock properties usually involve costly coring programs plus extensive laboratory efforts. An alternate method to estimate these rock properties is using well-logging methods, which represent significant technical as well as economic advantage. The purpose of this study is to enhance reservoir description of clean and shaly formations in both vertical and horizontal directions using well-logging data. A new approch has been developed for estimating the J-function in clean/shaly heterogeneous reservoirs. This newly developed correlation has been applied to field data, resulting in good matching. Based on leverett J-function and the new proposed approach for estimating J-function, a new correlation for estimating absolute permeability in the transitions zones has been developed. An investigation of permeability, porosity, and irreducible water saturation relationships leads to develop other two correlations in terms of cementation exponent, m, and saturation exponent, n, for estimating absolute permeability in the irreducible water saturation zones from well-logging data. The feasibility of evaluating permeability distribution of a heterogeneous formation utilizing geophysical well logs has also been investigated, Ben kahla field in Algeria has been selected as a study area. A methodology has been introduced for estimating permeability profile using core and geophysical well log data. Several vertical permeability relationships were obtained as a function of horizontal permeability, hydraulic mean radius, grain size, and the amount and/or type of shale. A procedure for determining vertical permeability from well log data is presented. The field data shows that the permeability correlation for predicting vertical and horizontal permeability can be established for a specific reservoir by using core permeability and well log data. Formation Permeability From Emperical Models Models to predict permeability in the oil column from porosity and other measurable rock parameters fall into three classes bases on either grain, surface area, or pore dimension considerations. Estimating permeabiliy in the transition zones In the oil column, it is the dimension of the connected pores that determine permeability, not grain size and sorting, nor porosity. Thus, all the methods that do not use pore dimension for estimating permeability are indirect methods. Rayman and Freeman3 proposed two correlations to calculate permeability from the displacement pressure and pore dimension. A new model capable of obtaining J-function using in-situ measurements in clean reservoirs has been developed in this section. The major advantages of this newly developed J-function are:Laboratory measurements of the capillary pressure, porosity and permeability have been eliminated,In-situ measurements of resistivity log (more representative to the reservoir rock) have been used, andThey are economically feasible and more effective.Equation 1 Eq. 1 represents new model for obtaining the J-function using in-situ measurements. Therefore, it is easy to estimate J-function at any interval in the transition zone knowing porosiy, formation factor and water saturation. Sw for clean formation can be estimated from Archie's equation. Estimating permeabiliy in the transition zones In the oil column, it is the dimension of the connected pores that determine permeability, not grain size and sorting, nor porosity. Thus, all the methods that do not use pore dimension for estimating permeability are indirect methods. Rayman and Freeman3 proposed two correlations to calculate permeability from the displacement pressure and pore dimension. A new model capable of obtaining J-function using in-situ measurements in clean reservoirs has been developed in this section. The major advantages of this newly developed J-function are:Laboratory measurements of the capillary pressure, porosity and permeability have been eliminated,In-situ measurements of resistivity log (more representative to the reservoir rock) have been used, andThey are economically feasible and more effective.Equation 1 Eq. 1 represents new model for obtaining the J-function using in-situ measurements. Therefore, it is easy to estimate J-function at any interval in the transition zone knowing porosiy, formation factor and water saturation. Sw for clean formation can be estimated from Archie's equation.

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The Hassi Massoud oil field is the largest of its kind in Algeria. The reservoir was discovered in 1956 and produces from a Cambrian-age at approximately 3400 meters depth. It produces 45°API oil from a thick Cambro-Ordovician sandstone formation. This sandstone is extremely hard, abrasive and slow to drill. The reservoir is naturally fractured in some parts. Fractures are either open or plugged with materials such as shale, silica, anhydrite, pyrite and bitumen. Porosity is ranging from 6 to 12%. Generally, the permeability is low with a range of less than 1 to more than 100 md in open-fractures layers Sonatrach introduced Underbalanced Drilling (UBD) primarily in an effort to improve penetration rates. However, all additional benefits obtained from UBD, such as production improvement and reservoir characterization while drilling, will be of an added value. Well OMPZ553 is the 37th well drilled underbalanced in the Hassi Massoud field. In this well, the focus was on production improvement with minimum formation damage while the increased rate of penetration (ROP) was a secondary benefit. Another objective was the evaluation of production while the well is being drilled. This eliminates the need for expensive post drilling production testing, and also to minimize borehole instability specially when drilling in the R2 section of the drain. In order to increase the success rate of drilling and completing this well underbalanced, Sonatrach introduced a new systematic and dynamic procedure. The new procedure consists of:Proper UBD candidate screeningCalculating the actual reservoir pressure before UB mode startsCompleting the well in UB mode This well proved to be the best UB drilled well in Hassi Massoud field in terms of reservoir benefits and characterization. The pre-job UBD candidate screening, feasibility studies and applying the new procedures proved effective in the success of this well. This paper describes in detail the above procedure and presents the successful application of such procedure to optimize production and enhance the ultimate recovery in the Hassi Massoud field. Lessons learnt and challenges encountered will also be discussed in this paper.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractPressure build-up data in low permeability reservoirs take too long and are usually of poor quality. It is often not economically feasible to shut in a well with a high production rate for a buildup test. Sand producing wells are not good candidates for long pressure drawdown tests. It is often impracticable to maintain a constant rate long enough to complete a drawdown test. In these cases, a multi-rate flow test should be run instead of buildup or drawdown tests. Actually a well-designed multi-rate flow test may minimize the influence of wellbore storage on pressure data.

The Hassi Massoud oil field is the largest of its kind in Algeria. The reservoir was discovered in 1956 and produces from a Cambrian-age at approximately 3400 meters depth. It produces 45°API oil from a thick Cambro-Ordovician sandstone formation. This sandstone is extremely hard, abrasive and slow to drill. The reservoir is naturally fractured in some parts. Fractures are either open or plugged with materials such as shale, silica, anhydrite, pyrite and bitumen. Porosity is ranging from 6 to 12%. Generally, the permeability is low with a range of less than 1 to more than 100 md in open-fractures layers Sonatrach introduced Underbalanced Drilling (UBD) primarily in an effort to improve penetration rates. However, all additional benefits obtained from UBD, such as production improvement and reservoir characterization while drilling, will be of an added value. Well OMPZ553 is the 37th well drilled underbalanced in the Hassi Massoud field. In this well, the focus was on production improvement with minimum formation damage while the increased rate of penetration (ROP) was a secondary benefit. Another objective was the evaluation of production while the well is being drilled. This eliminates the need for expensive post drilling production testing, and also to minimize borehole instability specially when drilling in the R2 section of the drain. In order to increase the success rate of drilling and completing this well underbalanced, Sonatrach introduced a new systematic and dynamic procedure. The new procedure consists of: Proper UBD candidate screening Calculating the actual reservoir pressure before UB mode starts Completing the well in UB mode This well proved to be the best UB drilled well in Hassi Massoud field in terms of reservoir benefits and characterization. The pre-job UBD candidate screening, feasibility studies and applying the new procedures proved effective in the success of this well. This paper describes in detail the above procedure and presents the successful application of such procedure to optimize production and enhance the ultimate recovery in the Hassi Massoud field. Lessons learnt and challenges encountered will also be discussed in this paper