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Exercise CHAPTER 6 Exercise SUBSURFACE ENVIRONMENT 1/ List the four types of subsurface waters, and give a one sentence definition for each Meteoric water Infiltration of rainwater Distribution @ shal[.]
CHAPTER Exercise SUBSURFACE ENVIRONMENT 1/ List the four types of subsurface waters, and give a one sentence definition for each -Meteoric water Infiltration of rainwater Distribution @ shallow depth Total mineralization: Low Tens to be Oxidizing pH: Often acidic due to dissolved humic, carbonic and nitrous acids -Connate water Ancient sea water which was trap in the sediment during burial Differs from seawater both in concentration of dissolved salt and pH, and Eh -Juvenile water Primary of magmatic origin Brought to near – surface environment dissolved in magma Usually mixed with either connate or meteoric water -Mixed water Results from the commingling of meteoric, juvenile and connate waters Usually between the near – surface meteoric water, juvenile and the deeper, more saline connate water 2/ a.) How does salinity vary with depth? - Depth the salinity high b.) What causes reversals of this vertical salinity trend? - Causes reversals of this vertical salinity trend is : depth, high geopressure + high temperature => water vapor and water increased and moved up -> minerals ione were kept in porosity -> high concentration -> high salinity 3/ Below is a listing of rock types or groups, label each according to their thermal conductivity characteristics Use the terms "high" , "variable" , or "low" Sandstone : variable Coal :low Limestone :variable Rock salt :high Anhydrite :high Dolomite :variable Shale - normal pressured :low Shale - overpressured :high What are the three main causes of regional variations in geothermal gradients? - First, there may be movements of deep, hot material to positions nearer the earth's surface These movements increase the thermal gradients and, therefore, the heat flow - Second, there may be large-scale movements of relatively cool, originally shallow rocks, to deeper positions within the earth, displacing hotter rocks at depth and causing lower gradients and heat flow - Third, there may he rock masses of great vertical extent but only limited lateral extent, which cause significant lateral contrasts In thermal conductivity, and so cause lateral variations in gradients and heat flow 5/ Why high geothermal gradients favor oil production? - Because, high geothermal gradients ( high temperature ) was ideal conditions for rock shale produced HC ( 150 – 2200C ), shales were changed to become material organic were original oil and primary porosity were preserved 6/ There are two basic types of subsurface pressures which together constitute the total overburden pressure What are they? • The fluid pressure, often called "pore pressure" or "formation pressure", is applied by the fluids within the pore spaces These fluids exert pressure against the grains • Lithostatic pressure is due to the weight of the rock overburden It is transmitted through the subsurface by grain-to-grain contacts in the rocks 7/ Below is a listing of causes of subnormal (under) or supernormal (over) pressures Label each with either the "underpressure" or overpressure" which they would cause _overpressure is caused by an artesian water system overpressure _ is caused by diagenesis, where water is expelled overpressure _ is caused by thermal expansion of water underpressure _ is caused by an increase in pore volume by decompression or fracturing overpressure _ is caused by under compaction of shale underpressure _ is caused by an increase in pore volume due to dissolution of mineral cements _underpressure is caused by a lowering of reservoir temperature 8*/ Sketch the potentiometric surface on the cross section ( Figure 1) 9*/ On this pressure/temperature graph for a crude oil/gas system, indicate the areas occupied by liquid, vapor, and liquid & vapor phase(s) Label the critical point, the bubble-point curve and the dew-point curve (Figure 2) 10*/ Below is a listing of basin characteristics, each belonging to either a "juvenile", "intermediate", or "senile" basin Mark each with a J for juvenile, I for intermediate, S for senile Juvenile basin_ dynamic fluid system, strong marine influences Senile basin_ widespread meteoric water in subsurface _ Intermediate basin _ meteoric water invasion at margins of basins _ _ Intermediate basin fluid pressures mostly hydrostatic, some artesian water systems senile basin generally only hydrostatic pressure gradients _ intermediate basin _ fluid movement compaction-induced, moving outwards towards margins _ juvenile basin invasion of meteoric water unimportant _ intermediate basin compaction of shales nearly complete juvenile basin overpressured shales common _ _ juvenile basin still actively receiving sediments _ intermediate basin mostly removed from marine influences _ intermediate basin oil beginning to be degraded at basin margins senile basin extensive degradation of oil _ 11/ There are 04 chemical composition relationships of ground water (classificated by Sulin-Russia) Determine the type and origin of them, What type would have most indication that relate to petroleum acummulation? >1; < and 1; > and 1; 1 and