US 12,291,963 B2
Estimation of fluid saturation of a formation from integration of multiple well logs
Chang-Yu Hou, Cambridge, MA (US); Lin Liang, Belmont, MA (US); Lalitha Venkataramanan, Lexington, MA (US); Harish Baban Datir, Tananger (NO); Austin Boyd, Ridgefield, CT (US); and Vasileios-Marios Gkortsas, Boston, MA (US)
Assigned to Schlumberger Technology Corporation, Sugar Land, TX (US)
Appl. No. 17/310,988
Filed by Schlumberger Technology Corporation, Sugar Land, TX (US)
PCT Filed Mar. 10, 2020, PCT No. PCT/US2020/021924
§ 371(c)(1), (2) Date Sep. 3, 2021,
PCT Pub. No. WO2020/185801, PCT Pub. Date Sep. 17, 2020.
Claims priority of provisional application 62/816,639, filed on Mar. 11, 2019.
Prior Publication US 2022/0082014 A1, Mar. 17, 2022
Int. Cl. E21B 49/00 (2006.01); E21B 47/12 (2012.01); G01V 3/34 (2006.01)
CPC E21B 49/005 (2013.01) [E21B 47/12 (2013.01); G01V 3/34 (2013.01); G01V 2210/66 (2013.01)] 14 Claims
OG exemplary drawing
 
1. A method of characterizing a formation traversed by a wellbore, the formation including at least a flushed zone and an uninvaded zone, the method comprising:
a) obtaining well log data based on a plurality of different well log measurements of the formation at multiple depths in the wellbore, the plurality of different well log measurements including:
a resistivity of the flushed zone;
a total porosity of the uninvaded zone; and
a water saturation of the flushed zone;
b) using the well log data of a) as inputs to a computational model that solves for a set of petrophysical parameters that characterize a portion of the formation corresponding to the multiple depths in the wellbore, the set of petrophysical parameters including a cementation exponent, a saturation exponent, and a flushed zone water resistivity;
c) using the set of petrophysical parameters solved for in b) to determine a value of water saturation of the uninvaded zone for the portion of the formation corresponding to the multiple depths in the wellbore; and
d) performing a wellbore drilling operation in accordance with the determined value of water saturation of the uninvaded zone,
wherein:
the computation model of b) minimizes a cost function that includes the well log data of a), and
the cost function can assume that the cementation exponent, the saturation exponent, and the flushed zone water resistivity are constant for the multiple depths, and wherein the cost function has a form of:

OG Complex Work Unit Math
where:
i represents N multiple depths from 1 to N,
RXO,i is resistivity of the flushed zone at each depth i,
m is the cementation exponent,
n is the saturation exponent,
Rw,XO is the water resistivity of the flushed zone,
ϕT,i is total porosity at each depth i,
Sw,XO,i is the water saturation of the flushed zone at each depth i, and
Rf( ) represents an Archie equation of a form of:
Rf(m,n,Rw,ϕT,Sw)=RwϕT−mSw−n, and
where:
Rw,XO is used for Rw, and
Sw,XO,i is used for Sw.