Apparatus and method for behind casing washout

A method for washing and plugging a wellbore, comprising:

• deploying a casing washout perforating gun assembly into a longitudinal section of a wellbore casing located within a wellbore, the casing washout perforating gun assembly including:
• a carrier gun body;
• a downhole plurality of charges supported within the carrier gun body;
• and
• an uphole plurality of charges supported within the carrier gun body;
• perforating a plurality of smaller downhole openings within the longitudinal section of the wellbore casing using the downhole plurality of charges, and a plurality of larger uphole openings within the wellbore casing using the uphole plurality of charges, the plurality of smaller downhole openings having downhole opening areas at least 20 percent less than uphole opening areas of the plurality of larger uphole openings;
• deploying a washing tool into the wellbore casing proximate the plurality of smaller downhole openings and plurality of larger uphole openings;
• pumping washing fluid through the washing tool radially outward into an annulus between the wellbore casing and the wellbore through the plurality of smaller downhole openings and retrieving excess washing fluid and debris from the annulus radially inward through the plurality of larger uphole openings, thereby cleaning the annulus;
• and
• pumping a fluidized plugging material through a work string into the wellbore casing proximate the longitudinal section, and thereby into the cleaned annulus, using one or more of the plurality of smaller downhole openings and plurality of larger uphole openings, to plug the wellbore casing and the cleaned annulus along at least a portion of the longitudinal section of the wellbore.

A well system, comprising:

• a wellbore casing located within a wellbore;
• a plurality of smaller downhole openings and a plurality of larger uphole openings located proximate one another within a longitudinal section of the wellbore casing, the plurality of smaller downhole openings having downhole opening areas at least 20 percent less than uphole opening areas of the plurality of larger uphole openings;
• and
• a cement plug located within at least a portion of the longitudinal section of the wellbore casing, the cement plug extending from an interior of the wellbore casing through the plurality of smaller downhole openings and the plurality of larger uphole openings and into an annulus between the wellbore casing and the wellbore.