For wells drilled with obm, dielectric scanner services waterfilled porosity yields the irreducible water saturation for the formation. The laboratory measurements of nuclear magnetic resonance nmr in conventional reservoirs. Interpretation of water saturation above the transitional zone in. Spe 109878 porelevel analysis of the relationship between. The new method for rock typing is verified with measurements acquired in two field cases of thick turbidite oil reservoirs. It is well recognized by operators in the hugoton, that determination of formation water saturations from induction wireline log response is problematic.
The advantage of this novel model is that s wirr can be. The coefficients of determination between the singularity strength range and petrophysical properties, in terms of porosity, permeability, rqi, fzi, irreducible water saturation, irreducible water porosity, t 2 cutoff, t 2lm, t 50, and t 35, are presented in table 4. Relationship between initial and residual lnapl saturation. The influencing factors of irreducible water saturation of sandstone reservoir and. This method could not be used effectively in this case because logbased water. Most reservoirs are water wet prior to oil migration and exhibit a long transition zone, through which saturation changes gradually from mostly oil with irreducible water at the top of the transition zone to water at the bottom.
In general, the irreducible water saturation increases as permeability decreases, as was shown in figure 8. It is difficult to calculate irreducible water saturation s wirr from nuclear magnetic resonance nmr logs in tight gas sands due to the effect of diffusion relaxation on the nmr t 2 spectrum at present. Based on the integration of relative permeability curve and mercury intrusion curve, the author studies the change regularity of the irreducible water saturation under different production conditions drawdown pressure, and puts forward the concept of dynamic irreducible water saturation and its determination method. Spe 115210 3 niobrara core sample tests reported a very high irreducible water saturation. In fact, the scal capillary pressure derived water saturation seemed to be at fault, seemingly the plugs werent desaturated to irreducible water saturation and capillary pressure equilibrium may not have been reached. Calculation of irreducible water saturation s wirr from. This can occur in transition zones between the oil and water leg, or after water influx into a reservoir due to production of oil or gas. Irreducible water saturation buckles method hydrocarbon zones with water saturation sw above irreducible saturation swir will produce some water along with hydrocarbons. Conventional departures from archie conditions for petrophysical attribute delineation include shaliness, fresh formation waters, thinbed reservoirs, and combinations of these cases. Relationship between initial and residual lnapl saturation for different soil types colin d.
Wireline logs of four 4 wells from apete field were studied to delineate petrophysical. Dielectric scanner salinityindependent water saturation. Dynamic irreducible water saturation and its determination. Johnston, csiro land and water, and mark adamski, pg, bp america abstract the residual saturation of light nonaqueous phase liquids lnapl plays an important role in determining lnapl movement, recoverability and remedial endpoints. Irreducible water saturation being a function of the rock characteristics. Irreducible water saturation and porosity sep 14, 2015. Fundamentals of fluid flow in porous media chapter 2 saturation in most oil formation it is believed that the formation was fully saturated with water prior to the oil migration and trapping in the formation. Combining semipermeable diaphragm method with nonsteady state method, bound water saturation and critical water saturation in du 38 district of daqing fuyang reservoir are determined before and after fracturing and relationship between them is also analyzed. These models are based on correlation between permeability, porosity and irreducible water saturation. Irreducible water saturation sometimes called critical water saturation. Spe 115210 irreducible water saturation has been determined.
The related term connate water saturation is the lowest water saturation found in situ. However, in the present situation, the injected water originates. In a reservoir at initial conditions, above the water contact, the irreducible saturation is equal to the actual or initial saturation, as found from conventional water saturation. The fraction of the pore space occupied by water when the hydrocarbon content is at maximum. Classically, the main uncertainty when calibrating water flooded zones comes from the water salinity. The less dense hydrocarbons are considered to migrate to positions of hydrostatic and dynamic equilibrium by displacing the initial. This level of water can only be reduced by flow of very dry gas that evaporates the water. The irreducible water saturation is less than 15% in oilwet rock and greater than 20% in waterwet rock. Pdf irreducible water saturation from capillary pressure. This present research utilizes well logs in the determination of permeability from one. Since the reservoir has been water flooded for nearly 30 years, a key data is the determination of the imbibition ri curves to estimate the water saturation in flooded zones.
For conventional hydrocarbons, the minimum value of the initial. Irreducible water saturationconstant the value of the power function, q, ranges from about 0. Irreducible water saturation sometimes called critical water saturation defines the maximum water saturation that a formation with a given permeability and porosity can retain without producing water. In order to calculate water cut, the irreducible water saturation swirr has to be defined beforehand. These test results can be substantiated by the fact that the niobrara does not make any formation water at the wattenberg field.
Sw constant porosity, but the constant can vary with pore geometry. This water, although present, is held in place by capillary forces and will not flow. Pdf it is difficult to calculate irreducible water saturation s wirr from nuclear magnetic resonance nmr logs in tight gas sands due to the effect. Pdf irreducible water saturation value is an indication of total volume of oil and.
Water saturation s w determination is the most challenging of petrophysical calculations and is used to quantify its more important complement, the hydrocarbon saturation 1 s w. Relationship between porosity and water saturation. Crains petrophysical handbook irreducible water saturation. The irreducible saturation of the wetting phase before wettability alteration airbrine system for water wet sample is smaller than the irreducible saturation of the wetting phase after the wettability of the samples were changed to oilwet airoil system as shown in figures and 14. Three methods are usu ally taken in laboratory to establish the irreducible water saturation. If these departures are unrecognized, water saturation can be overestimated, and this can result in loss of opportunity. Relationship between porosity and water saturation search and. Productive waterwet sandstones usually have irreducible water saturations between 20% and 40%. Determining irreducible water saturation based on well log data and. Determination of relative permeability curves in the arbuckle. The accurate determination of irreducible water saturation will result in more reliable and precise well log data interpretation, which will impact the estimation of reservoir resources of oil and gas.
Connate water saturation an overview sciencedirect topics. Irreducible water saturation an overview sciencedirect topics. Chapter four fluid saturations saturation is defined as that fraction, or percent, of the pore volume occupied by a particular fluid oil, gas, or water. Stateoftheart in permeability determination from well log data. Determination of irreducible water saturation and its. Discussion on the irreducible water saturation and ultralow. There are usually sufficient reservoir data to determine the irreducible water saturation including. Pdf irreducible water saturation and porosity mathematical. Connate water saturation s w and flushed zone water saturation s xo can be calculated from information supplied by well logs.
This property is expressed mathematically by the following relationship. Complexities arise because there are a number of independent approaches that can be used to calculate s w. Discussion on the irreducible water saturation and ultra. Determining irreducible water saturation based on well log. In addition, because pores and pore channels are equally small, for all practical purposes clay shells exhibit zero permeability. Defining irreducible water saturation using global characteristics. Yet, laboratory measurements for determining irreducible water saturation take considerable. Determination of connate water saturation with a rock centrifuge in the hydrocarbon industry, a frequently applied method of connate water saturation determination is obtaining the capillary pressure curve by a rock centrifuge measurement. Connate water saturation is the fraction of pore volume in an undisturbed formation filled with connate water. The term is somewhat imprecise because the irreducible water saturation is dependent on the final drive pressure when flowing oil or gas or the maximum speed of rotation in a centrifuge.
Water held in this shell is responsible for presence of irreducible water saturation. Discussion on the irreducible water saturation and ultralow water saturation international organization of scientific research 67 p a g e constantly, reservoir have more bound water is vaporized, continuously along with the transport of natural gas. Irreducible water saturation value is an indication of total volume of oil and water producible from a reservoir. Values of q and the constant are easily derived by plotting the log of porosity vs. Irreducible water saturation buckles method many permeability calculation models based on log analysis require knowledge of the irreducible water saturation. Subsurface and petrophysical studies of shalysand reservoir. The determination of the connate water saturation is performed on rock samples prepared in this way. Effect of wettability on capillary pressure the capillary pressure saturation relationship depends on the interaction of wettability, pore structure, initial saturation, and saturation history. Irreducible water saturation varies inversely with porosity. It also influences the production rate from that reservoir. Pdf calculation of irreducible water saturation s wirr from nmr. The difference between sw and swir, and relative permeability of water and hydrocarbon. Wettability effects on capillary pressure, relative. Case study formation evaluation dielectric scanner service provides salinityindependent water saturation for gas shale analysis accurate waterfilled porosity now possible in complex lithology.
Equations 7 and 9 could be used for permeability determination in all of the wells, if reliable initial water saturation existed in these wells initial water saturation can be converted to irreducible water saturation by pc equations. Swi initial or connate water saturation, dimensionless bo oil formation volume factor, m3sm3. By combining with classical timur and schlumbergerdoll research sdr models, a novel model of calculating s wirr is derived. Petrophysical characterization of carbonate naturally. Applications of the lucia method in carbonate petrophysics. In reservoir rocks, there are formation water which cannot be replaced by the oil and gas migrating to the reservoir rocks er saturation is called irreducible water saturation swirr. A reservoir with sw swir will produce some water with the hydrocarbons. The key to reliable hydraulic rock typing in reservoirs straddling multiple capillary windows article pdf available september 20 with 1,365 reads.
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