Floating controllable surveillance balls for monitoring wellbore parameters

A method of monitoring one or more wellbore parameters in a wellbore, comprising:

• conveying a floating controllable surveillance ball into a wellbore filled with a wellbore fluid and extending from a wellhead installation, the floating controllable surveillance ball including:
• a body having a density less than a density of the wellbore fluid;
• and
• a dissolvable material arranged in a plurality of annular rings disposed about an outer circumference of the body and dissolvable in the presence of the wellbore fluid, wherein a combined density of the body and the dissolvable material is greater than the density of the wellbore fluid;
• reacting a first portion of the dissolvable material provided in a first annular ring of the plurality of annular rings with the wellbore fluid and thereby dissolving the first portion;
• decreasing the combined density as the first portion dissolves and thereby causing the floating controllable surveillance ball to ascend uphole and stop at a first level within the wellbore, wherein the floating controllable surveillance ball remains stationary at the first level while the combined density equals the density of the wellbore fluid at the first level;
• reacting a second portion of the dissolvable material provided in a second annular ring of the plurality of annular rings with the wellbore fluid at the first level and thereby dissolving the second portion;
• and
• decreasing the combined density of the floating controllable surveillance ball as the second portion dissolves and thereby causing the floating controllable surveillance ball to ascend uphole and stop a second level within the wellbore, wherein the floating controllable surveillance ball remains stationary at the second level while the combined density equals the density of the wellbore fluid at the second level.

A floating controllable surveillance ball, comprising:

• a spherical body that defines an interior;
• one or more sensors arranged within the interior and operable to obtain one or more wellbore parameters within a wellbore filled with a wellbore fluid;
• and
• a dissolvable material arranged in a plurality of annular rings disposed about an outer circumference of the body and dissolvable in the presence of the wellbore fluid,
• wherein a combined density of the body and the dissolvable material is greater than a density of the wellbore fluid and thereby allows the floating controllable surveillance ball to descend to a bottom of the wellbore under gravitational forces, and
• wherein dissolving the dissolvable material in the wellbore fluid progressively decreases the combined density, thereby causing the floating controllable surveillance ball to float back to the wellhead installation for retrieval, and
• wherein dissolution of each annular ring in the wellbore fluid progressively decreases a combined density of the floating controllable surveillance ball, thereby controlling an ascent trajectory of the floating controllable surveillance ball within the wellbore.