Optimized well spacing for in situ shale oil development

Abstract

A method for spacing heater wells for an in situ conversion process is provided. The method includes the steps of determining a direction along which thermal energy will travel most efficiently through a subsurface formation, and completing a plurality of heater wells in the subsurface formation, with the heater wells being spaced farther apart in the determined direction than in a direction transverse to the determined direction. In one aspect, the step of determining a direction along which thermal energy will travel most efficiently is performed based upon a review of geological data pertaining to the subsurface formation. The geological data may comprise the direction of least horizontal principal stress in the subsurface formation. Alternatively, the geological data may comprise the direction of bedding in the subsurface formation, the tilt of the subsurface formation relative to the surface topography, the organic carbon content of the kerogen, the initial formation permeability, and other factors.

1 . A method for spacing heater wells for an in situ conversion process in a subsurface formation comprising oil shale, the method comprising:
 determining a direction along which thermal energy will travel most efficiently through the subsurface formation; and   completing a plurality of heater wells in the subsurface formation, the heater wells being spaced farther apart in the determined direction than in a direction transverse to the determined direction.   
   
   
       2 . The method of  claim 1 , wherein the step of determining a direction along which thermal energy will travel through the subsurface formation most efficiently is performed based upon a review of geological data pertaining to the subsurface formation. 
   
   
       3 . The method of  claim 2 , wherein the geological data comprises the direction of least horizontal principal stress in the subsurface formation. 
   
   
       4 . The method of  claim 3 , wherein the direction along which thermal energy will travel through the subsurface formation most efficiently is substantially perpendicular to the direction of least horizontal principal stress. 
   
   
       5 . The method of  claim 3 , wherein the direction along which thermal energy will travel through the subsurface formation most efficiently is substantially parallel to the direction of least horizontal principal stress. 
   
   
       6 . The method of  claim 2 , wherein the geological data comprises the direction of bedding in the subsurface formation. 
   
   
       7 . The method of  claim 6 , wherein the direction along which thermal energy will travel through the subsurface formation most efficiently is substantially along the direction of bedding of the subsurface formation. 
   
   
       8 . The method of  claim 2 , wherein the geological data comprises the tilt of the subsurface formation and the relative spacing with the surface topography. 
   
   
       9 . The method of  claim 8 , wherein the direction along which thermal energy will travel through the subsurface formation most efficiently is along a direction of upward tilt of the subsurface formation relative to the surface topography. 
   
   
       10 . The method of  claim 8 , wherein the direction along which thermal energy will travel through the subsurface formation most efficiently is along a direction of upward tilt of the subsurface formation relative to sea level. 
   
   
       11 . The method of  claim 8 , wherein the direction along which thermal energy will travel through the subsurface formation most efficiently is along a direction of shortest relative distance between the local plane of the subsurface formation and the local plane of the surface topography. 
   
   
       12 . The method of  claim 8 , wherein the direction along which thermal energy will travel through the subsurface formation most efficiently is along a direction of shortest relative distance between the local plane of the subsurface formation and sea level. 
   
   
       13 . The method of  claim 1 , wherein the step of determining a direction along which thermal energy will travel through the subsurface formation most efficiently is performed based upon a review of formation temperature gradient data from previous in situ conversion processes in other areas of the subsurface formation. 
   
   
       14 . The method of  claim 1 , wherein the geological data comprises at least one of the organic carbon content of the kerogen, hydrogen index of the subsurface formation, initial formation permeability, depth of the subsurface formation, thickness of the subsurface formation, heterogeneity of rock in the subsurface formation, and modified Fischer Assay analyses. 
   
   
       15 . The method of  claim 1 , wherein the heater wells are substantially vertical. 
   
   
       16 . The method of  claim 1 , wherein:
 the plurality of heater wells are completed with a substantially horizontal wellbore, the horizontal wellbores being substantially parallel to each other; and   each horizontal wellbore is completed substantially in the direction of least horizontal principal stress in the subsurface formation.   
   
   
       17 . The method of  claim 1 , wherein:
 the plurality of heater wells are completed with a substantially horizontal wellbore, the horizontal wellbores being substantially parallel to each other; and   each horizontal wellbore is completed substantially in a direction normal to the least horizontal principal stress in the subsurface formation.   
   
   
       18 . The method of  claim 1 , wherein:
 selected first heater wells have a horizontal wellbore completed at a first depth in the subsurface formation, and selected second heater wells have a horizontal wellbore completed at a second depth in the subsurface formation; and   the first and second heater wells are alternatingly spaced within the subsurface formation, and are spaced farther apart horizontally than vertically.   
   
   
       19 . The method of  claim 1 , further comprising:
 heating the subsurface formation in order to form thermally induced fractures.   
   
   
       20 . The method of  claim 2 , further comprising the steps of:
 completing at least one production well through the subsurface formation;   producing hydrocarbons through the at least one production well; and   wherein the at least one production well comprises a plurality of production wells also aligned in the determined direction.   
   
   
       21 . The method of  claim 1 , wherein:
 the plurality of heater wells comprise sets of a repeating well pattern elongated in the determined direction;   each set of repeating well patterns has a production well completed through the surface formation; and   the sets of well patterns each have a production well completed through the surface formation.   
   
   
       22 . The method of  claim 21 , wherein the patterns of heater wells are 3-spot patterns, 5-spot patterns, 6-spot patterns or 7-spot patterns. 
   
   
       23 . The method of  claim 21 , wherein the patterns of heater wells comprise a first pattern around a corresponding production well, and a second pattern around the first pattern. 
   
   
       24 . The method of  claim 21 , wherein the repeating well pattern elongated in the determined direction defines an elongation ratio of about 1.20 to 2.50. 
   
   
       25 . A method for arranging heater wells for an in situ kerogen conversion process, comprising:
 providing a production well;   completing a plurality of heater wells around the production well, the plurality of heater wells comprising a first layer of heater wells around the production well, and a second layer of heater wells around the first layer;   wherein the heater wells in the second layer of wells are arranged relative to the heater wells in the first layer of wells so as to minimize secondary cracking of hydrocarbons converted from the kerogen as the hydrocarbons flow from the second layer of wells to the production well; and   wherein the plurality of heater wells and the production well are arranged such that the majority of hydrocarbons generated by heat from each heater well is able to migrate to the production well without passing through a zone of substantially increasing formation temperature.