Method and apparatus for producing unconventional oil at shallow depths

Abstract

An oil production well is drilled into a kerogenous chalk source rock comprising (i) type IIs kerogen and (ii) shallow naturally-occurring unconventional oil derived from the type IIs kerogen that is resident within pore space of the source rock. In some embodiments, the production well is drilled at a location where the geothermal gradient is at least 3 degrees C. per 100 m is present at or near the production well. It is believed that the presence of this geothermal gradient accelerated maturation of the type IIs kerogen of the source rock to convert a portion of the type IIs kerogen into the unconventional oil. In some embodiments, the shallow production well is non-vertical. In some embodiments, at depths that are shallow and within the source rock, the production well is cased and perforated. Oil from the source rock may be produced via the production well and the shallow-depth perforated locations thereof.

What is claimed: 
     
         1 . A method of unconventional oil production comprising:
 a. drilling a production well into a kerogenous chalk source rock comprising (i) type IIs kerogen and (ii) shallow naturally-occurring unconventional oil derived from the type IIs kerogen that is resident within pore space of the source rock;   b. at shallow depths of at most 2 kilometers and within the source rock, casing and perforating the production well; and   c. producing the shallow naturally-occurring unconventional oil from the source rock via the production well.   
     
     
         2 . The method of  claim 1  wherein a location at which the production well is drilled is selected in accordance with a geothermal gradient. 
     
     
         3 . The method of any preceding claim wherein the production well is drilled at a location where the geothermal gradient is at least 3.0 degrees Celsius per 100 meters, or at least 3.5 degrees Celsius per 100 meters, or at least 4.0 degrees Celsius per 100 meters. 
     
     
         4 . The method of any preceding claim wherein the unconventional oil and at least some of the perforations of the production well are located at depths of at most 1.5 kilometers, or at most 1200 meters, or at most 1 kilometer or at most 800 meters. 
     
     
         5 . The method of any preceding claim wherein the source rock is below an overburden comprising a basalt layer. 
     
     
         6 . The method of  claim 5  wherein the overburden further comprises a sedimentary portion situated below the basalt layer so that horizontal stresses of the sedimentary portion were locked in at or before a time of deposition of the lava flow which formed the basalt layer. 
     
     
         7 . The method of any preceding claim wherein a porosity of the source rock is at least 30% or at least 35% or at least 40%. 
     
     
         8 . The method of any preceding claim wherein a permeability of the source rock matrix is at most 1 mD or at most 0.1 mD or at most 0.01 mD. 
     
     
         9 . The method of any preceding claim wherein an oil saturation of pore space of the source rock is at least 50% or at least 60% or at least 70%. 
     
     
         10 . The method of any preceding claim wherein the source rock is stimulated at the shallow depths to increase a permeability of the source rock. 
     
     
         11 . The method of  claim 10  wherein the stimulation of the source rock occurs at a depth that is less than that of all aquifers thereof. 
     
     
         12 . The method of any of  claims 10 - 11  wherein the source rock is stimulated by means other than by hydraulic stimulation. 
     
     
         13 . The method of any preceding claim wherein a total organic content (TOC) of the source rock is at least 10%. 
     
     
         14 . The method of any preceding claim wherein the source rock is stimulated at the shallow depths by high pressure acid stimulation of the source rock. 
     
     
         15 . The method of any preceding claim wherein the source rock is hydraulic stimulated. 
     
     
         16 . The method of any preceding claim wherein the source rock thermally stimulated. 
     
     
         17 . The method of  claim 16  wherein thermal energy is effective to significantly increase the mobility of the naturally-occurring oil by at least a factor of 10. 
     
     
         18 . The method of any of  claims 16 - 17  wherein thermal energy is effective to significantly decrease the viscosity of the naturally-occurring oil by at least a factor of 10. 
     
     
         19 . The method of any of  claims 16 - 18  wherein the thermal energy is effective to vaporize liquid water and light hydrocarbons within the pore space of the source rock. 
     
     
         20 . The method of any preceding claim wherein pressurized steam is injected into the source rock at the shallow depths so as to thermally stimulate the source rock to increase a mobility of the unconventional oil. 
     
     
         21 . The method of  claim 20  wherein the steam is injected according to a huff-and-puff technique. 
     
     
         22 . The method of any of  claims 20 - 21  wherein the steam enters the source rock at a temperature of at most 200 degrees Celsius. 
     
     
         23 . The method of any preceding claim wherein the production well is non-vertical. 
     
     
         24 . The method of  claim 23  wherein the non-vertical production well is substantially horizontally-oriented. 
     
     
         25 . The method of any of  claims 23 - 24  wherein the stimulation forms a plurality of parallel, thin flow channels within the source rock that are each substantially vertically oriented, a thickness direction of the flow channels being along a central axis of the production well, and with each flow channel leading to the production well. 
     
     
         26 . The method of any preceding claim wherein the production well is substantially horizontal, a central axis thereof being substantially parallel to a minimum stress vector of the kerogenous chalk source rock. 
     
     
         27 . The method of any preceding claim wherein a total organic content (TOC) of the source rock is at least 15%. 
     
     
         28 . The method of any preceding claim wherein a sulfur content of the unconventional oil is at least 2.5% wt/wt or at least 3% wt/wt or at least 3.5% wt/wt or at least 4% wt/wt. 
     
     
         29 . The method of any preceding claim wherein an API gravity of the unconventional oil is at least 20° and/or at most 30°. 
     
     
         30 . The method of any preceding claim wherein a maximum depth of the production well is at most 2 km or at most 1.5 kilometers, or at most 1200 meters, or at most 1 kilometer or at most 800 meters. 
     
     
         31 . The method of any preceding claim wherein oil produced via the production wells is never heated within the source rock to a temperature exceeding 200 degrees Celsius 
     
     
         32 . The method of any preceding claim, carried out so that bulk source rock is never heated to a temperature exceeding 200 degrees Celsius. 
     
     
         33 . The method of any preceding claim wherein the method is carried out without significantly pyrolyzing the source rock. 
     
     
         34 . The method of any preceding claim wherein a majority of hydrocarbon liquids produced via the production wells is the naturally-occurring oil. 
     
     
         35 . The method of any previous claim, wherein the producing includes drawing naturally-occurring oil residing in pore space of the kerogenous chalk source rock into the production well. 
     
     
         36 . The method of any previous claim, wherein the producing includes drawing naturally occurring oil residing in the pore space of the kerogenous chalk source rock into the production well via perforations thereof. 
     
     
         37 . The method of any previous claim, further comprising subjecting the produced oil to a distillation process. 
     
     
         38 . The method of any previous claim, further comprising desulfurizing the produced oil or a derivative thereof. 
     
     
         39 . The method of any previous claim, further comprising refining the produced oil into at least one of naphtha, gasoline, diesel fuel, asphalt base, heating oil, kerosene, and liquefied petroleum gas. 
     
     
         40 . The method of any previous claim wherein a geothermal gradient at one or more candidate locations is analyzed, and the drilling of the production well at its location is contingent upon the results of the analysis. 
     
     
         41 . The method of any previous claim wherein the kerogenous chalk is situated beneath a basalt overburden. 
     
     
         42 . The method of  claim 41  wherein a thickness of the basalt overburden at one or more candidate locations is analyzed, and the drilling of the production well at its location is contingent upon the results of the analysis. 
     
     
         43 . The produced oil, or any derivative thereof, produced by the method of any of preceding claim. 
     
     
         44 . An apparatus for unconventional oil production comprising:
 a production well drilled into a kerogenous chalk source rock comprising (i) type IIs kerogen and (ii) shallow naturally-occurring unconventional oil derived from the type IIs kerogen that is resident within pore space of the source rock, wherein the production well is cased and perforated at shallow depths of at most 2 kilometers and within the source rock so that the shallow naturally-occurring unconventional oil is recovered by the production well via the shallow-depth perforations of the production well.   
     
     
         45 . The apparatus of  claim 44  wherein the production well is non-vertical. 
     
     
         46 . The apparatus of  claim 44  wherein the production well is horizontal. 
     
     
         47 . The apparatus of any of  claims 44 - 46  further comprising a series of thin parallel flow channels that are all vertically oriented and transverse to a central axis of the production well. 
     
     
         48 . The apparatus of any of  claims 44 - 47  wherein the production well is substantially horizontal, a central axis thereof being substantially parallel to a minimum stress vector of the kerogenous chalk. 
     
     
         49 . The apparatus of any of  claims 44 - 48  wherein at a location of the production well, a local geothermal gradient is at least 3.0 degrees Celsius per 100 meters, or at least 3.5 degrees Celsius per 100 meters, or at least 4.0 degrees Celsius per 100 meters. 
     
     
         50 . The apparatus of any of  claims 44 - 49  wherein the unconventional oil and at least some of the perforations of the production well are located at depths of at most 1.5 kilometers, or at most 1200 meters, or at most 1 kilometer or at most 800 meters. 
     
     
         51 . The apparatus of any of  claims 44 - 50  wherein the source rock is below an overburden comprising a basalt layer. 
     
     
         52 . The apparatus of any of  claims 44 - 51  wherein the overburden further comprises a sedimentary portion situated below the basalt layer so that horizontal stresses of the sedimentary portion were locked in at or before a time of deposition of the lava flow which formed the basalt layer. 
     
     
         53 . The apparatus of any of  claims 44 - 52  wherein a porosity of the source rock is at least 30% or at least 35% or at least 40%. 
     
     
         54 . The apparatus of any of  claims 44 - 53  wherein a permeability of the source rock matrix at most 1 mD or is at most 0.1 mD or at most 0.01 mD. 
     
     
         55 . The apparatus of any of  claims 44 - 54  wherein an oil saturation of pore space of the source rock is at least 50% or at least 60% or at least 70%. 
     
     
         56 . The apparatus of any of  claims 44 - 55  wherein a total organic content (TOC) of the source rock is at least 15%. 
     
     
         57 . The apparatus of any of  claims 44 - 56  wherein a sulfur content of the unconventional oil is at least 2.5% wt/wt or at least 3% wt/wt or at least 3.5% wt/wt or at least 4% wt/wt. 
     
     
         58 . The apparatus of any of  claims 44 - 57  wherein an API gravity of the unconventional oil is at least 25° and/or at most 30°.