Connate water

D, 8 0 and Cl concentration data suggest the mixing of meteoric water, connate seawater and magmatic gas (Seki, 1991) (Fig. 2.20). Br/Cl and B/Cl ratios are different from those of seawater (Fig. 2.21). This difference and N2-H2-Ar gas composition indicate a contribution of magmatic gas (Seki, 1991, 1996). 

Einsele, G., 1976. Rise of primary pore water (connate water) in compacting sediments. In Hydrogeology of Great Sedimentary Basins. Int. Hydrol. Conference, Budapest, 1976, pp. 134-135... 

Lane, A. C. (1927). Calcium Chloride Waters, Connate and Diagenetic. Bull., Am. Assoc. Petrol. Geol. 11(12), 1283-1305. 

Poorly sorted sediments comprise very different particle sizes, resulting in a dense rock fabric wifh low porosify. As a resulf the connate water saturation is high, leaving little space for the storage of hydrocarbons. Conversely, a very well sorted sediment will have a large volume of space between the evenly sized components, a lower connate water saturation and hence a larger capacity to store hydrocarbons. Connate water is the water which remains in the pore space after the entry of hydrocarbons. 

Solution gas drive occurs in a reservoir which contains no initial gas cap or underlying active aquifer to support the pressure and therefore oil is produced by the driving force due to the expansion of oil and connate water, plus any compaction drive.. The contribution to drive energy from compaction and connate water is small, so the oil compressibility initially dominates the drive energy. Because the oil compressibility itself is low, pressure drops rapidly as production takes place, until the pressure reaches the bubble point. 

Gas reservoirs are produced by expansion of the gas contained in the reservoir. The high compressibility of the gas relative to the water in the reservoir (either connate water or underlying aquifer) make the gas expansion the dominant drive mechanism. Relative to oil reservoirs, the material balance calculation for gas reservoirs is rather simple. A major challenge in gas field development is to ensure a long sustainable plateau (typically 10 years) to attain a good sales price for the gas the customer usually requires a reliable supply of gas at an agreed rate over many years. The recovery factor for gas reservoirs depends upon how low the abandonment pressure can be reduced, which is why compression facilities are often provided on surface. Typical recovery factors are In the range 50 to 80 percent. 

The above experiment was conducted for a single fluid only. In hydrocarbon reservoirs there is always connate water present, and commonly two fluids are competing for the same pore space (e.g. water and oil in water drive). The permeability of one of the fluids is then described by its relative permeability (k ), which is a function of the saturation of the fluid. Relative permeabilities are measured in the laboratory on reservoir rock samples using reservoir fluids. The following diagram shows an example of a relative permeability curve for oil and water. For example, at a given water saturation (SJ, the permeability... 

The specific microbes used depends on many factors, for example, the particular formation involved, the specific hydrocarbons in the formation, and the desired microbial action on these formation hydrocarbons. The microbes may be aerobic or anaerobic and may or may not require one or more additional nutrients (e.g., naturally ocurring or injected) to be included in the formation. Highly mobile microbes, such as flagellated or ciliated bacilli, are useful. The microbes are sized so that they are mobile in the connate water of the formation [966]. 

Formation damage caused by clay migration may be observed when the injected brine replaces the connate water during operations such as water-flooding, chemical flooding including alkaline, and surfactant and polymer processes. These effects can be predicted by a physicochemical flow model based on cationic exchange reactions when the salinity decreases [1665]. Other models have also been presented [345,1245]. 

Epithermal Low temperatures (< 300 °C) and pressures, farthest from the intrusive, mixed with connate and meteroric waters Gold, silver, mercury, antimony, arsenic, bismuth, selenium, lead, zinc... 

Telethermal Essentially meteoric and connate waters with little addition of magmatic water, very low temperatures (< 100 °C) and pressures, near the surface Lead, zinc, cadmium germanium... 

The Eh of connate waters (water entrapped in the interstices of sediment at the time of deposition) ranges from 0 to -200 mV. For example, formation water from two monitoring wells in the lower limestone of the Florida aquifer near Pensacola ranged from +23 to -32 mV,67 and formation fluids from a Devonian limestone in Illinois used for injection at a depth of about 3200 ft had an Eh of -154 mV.16... 

Effect of Ca2. In many reservoirs the connate waters ontain substantial quantities of divalent ions (mostly Ca . In alkaline flooding applications at low temperatures, the presence of divalent ions leads to a drastic increase in tensions r35,36]. Kumar et al. f371 also found that Ca and Mg ions are detrimental to the interfacial tensions of sulfonate surfactant systems. Detailed studies at elevated temperatures appear to be non-existent. 

Crude Oils and Connate Water. The multiple micellar slug process was developed for the tertiary recovery of three light oils viz. Bradford crude, Bonnie Glen crude and Provost crude. The viscosities and densities of the three crude oils used are listed in Table I. 

A 2% (w/v) sodium chloride solution was used as the connate water in all corefloods. It should be mentioned that it is desirable to incorporate divalent cations, such as Ca++ and Mg++, in the slug formulations as well as in the connate water to simulate an actual reservoir. 

For the wet case, the foam enters and achieves steady state after several pore volumes. A mobility reduction compared to water of about 90% ensues. However, for the dry case, there is about a one pore-volume time lag before the pressure responds. During this time, visual observations into the micromodel indicate a catas-tropic collapse of the foam at the inlet face. The liquid surfactant solution released upon collapse imbibes into the smaller pores of the medium. Once the water saturation rises to slightly above connate (ca 30%), foam enters and eventually achieves the same mobility as that injected into the wet medium. 

The chloride content of groundwater may be a sensitive indicator of either the distance between the intake area of the aquifer and coast or the amount of evapotranspiration prior to groundwater recharge. Because chloride is not normally derived from dissolution of solid aquifer materials and it does not enter into ion exchange reactions to any great extent, the chloride content in shallow aquifers and aquifers isolated from sources of connate water should reflect some of the original environmental factors of the outcrop area [19,86]. 

Oxygen and hydrogen isotopes are a powerful tool in the study of the origin of subsurface waters. Prior to the use of isotopes, it was generally assumed that most of the formation waters in marine sedimentary rocks were of connate marine origin. This widely held view was challenged by Clayton et al. (1966), who demonstrated that waters from several sedimentary basins were predominantly of local meteoric origin. 

Presently, in the view of numerous subsequent studies, (i.e., Hitchon and Friedman 1969 Kharaka et al. 1974 Banner et al. 1989 Connolly et al. 1990 Stueber and Walter 1991), it is obvious that basin subsurface waters have complicated histories and frequently are mixtures of waters with different origins. As was proposed by Knauth and Beeunas (1986) and Knauth (1988), formation waters in sedimentary basins may not require complete flushing by meteoric water, but instead can result from mixing between meteoric water and the remnants of original connate waters. 

The carbonaceous and nitrogenous components in peat and in the connate waters were determined by Motojima (13) and Maki (12) and the results are given in Tables IX and X. The relationship between the ratios of Total C/ Total N of peat and those of the connate waters suggests that the same micro-... 

Table X. Vertical Variation of Carbon and Nitrogen of Connate Waters in Peat from Higashiyonesato ...

Water invariably occurs with petroleum deposits. Thus, a knowledge of the properties of this connate, or interstitial, or formation water is important to petroleum engineers. In this chapter, we examine the composition of oilfield water water density, compressibility, formation volume factor and viscosity solubility of hydrocarbons in water and solubility of water in both liquid and gaseous hydrocarbons and, finally, water-hydrocarbon interfacial tension. An unusual process called hydrate formation in which water and natural gas combine to form a solid at temperatures above the freezing point of water is discussed in Chapter 17. 

CONNATE WATER. Water that is trapped in marine sediments at the time they are laid down in the sea is commonly called commie Hater. As the term implies, connate water is produced at the same lime as the rock and constitutes a sort of fossil seawater. 

Many geological processes may have modified the composition of connate brines to produce iheir wide range. Obviously these alterations have been extensive. Some connate waters are essentially saturated... 

Analyses of a variety of connate brines have been published by White, Hem, and Waring (19631. White (1957) has suggested criteria for distinguishing connate water by means of ratios of concentrations of certain of the dissolved ions to one anulher. In most cunnalc water the ratios of bromide and iodide to chlorine are relatively high and ratios of potassium and lithium to sodium are low. 

Thus gas, if any is present, is found in the highest parts of the trap, followed by oil (and oil with gas) below the gas, and finally salt water below the oil. Experience has indicated that the salt water seldom was completely displaced by oil or gas from the pore spaces, even w ithin the trap. Even in the midst of oil and gas accumulation, pore spaces within the trap may contain from 10 to 50% or more of salt water, It appears that the remaining water (termed connate water) fills the smaller pores ancl also exists as a coating or film, covering the rock surfaces of the larger pore spaces thus oil and/or gas are apparently contained in water-jacketed pore spaces. The geological structures called traps are petroleum reservoirs, i.e.. they are the oil and gas fields that me explored and produced. All oil fields contain some gas, but the quantity may range widely. See also Natural Gas. 

Many of the scientific aspects of water resources are described in several entries in this encyclopedia. See also Connate Water Desalination Groundwater and Water Pollution. 

---