System and method for estimating porosity distribution in subterranean reservoirs

1) A computer-implemented method for estimating porosity distribution in a region of interest of a geologic formation, from a resistivity image log representative of the geologic formation, the method comprising:

• a. calculating a normalization factor representative of a rock matrix based on a first resistivity value using
• (
• 1
• -
• v
• -
• V
• tight
• V
• total
• )
• ×
• 〈
• 1
• r
• 1
• 
• /
• 
• m
• 〉
• ma
• where ν is a fractional volume representing a secondary porosity, Vtight is a volume of the rock formation of interest which is occupied by rock with substantially zero porosity, Vtotal is a volume of rock formation of interest, and
• 〈
• 1
• r
• 1
• 
• /
• 
• m
• 〉
• ma
• =
• 1
• N
• ma
• 
• ∑
• j
• =
• 1
• N
• ma
• 
• 1
• r
• j
• 1
• 
• /
• 
• m
• where Nma is a number of cells in a volume of rock formation of interest which are occupied by the rock matrix, m is a cementation factor, and rj is the resistivity image value at cell j and is not smaller than the first resistivity value, which is used to define cells belonging to the rock matrix;
• b. calculating an image point factor based on a second resistivity value using
• (
• φ
• -
• φ
• v
• )
• ×
• 1
• r
• i
• 1
• 
• /
• 
• m
• where φ is a reference porosity, φν is the secondary porosity, m is a cementation factor, and ri is the second resistivity value;
• c. comparing the image point factor and the normalization factor to identify points in the resistivity image log that correspond to the secondary porosity;
• d. recalculating the normalization factor and the image point factor based on a different first resistivity value and a different second resistivity value;
• e. re-comparing the recalculated normalization factor and the recalculated image point factor to identify additional points in the resistivity image log that correspond to the secondary porosity;
• and
• f. repeating the recalculating and re-comparing steps until a termination criterion is met, wherein the termination criterion is met when either the image point factor for the rock matrix part of the region of interest is smaller than the normalization factor or the secondary porosity ceases to be smaller than the reference porosity.