Controlled pneumatic well pumping system, and method for optimizing pump stroke speed

A pneumatic pumping system for a wellbore, comprising:

• a cylinder defining an elongated tubular body disposed vertically over the wellbore;
• an elongated polished rod residing substantially within the cylinder;
• a piston connected to the polished rod that is movable between upper and lower positions within the cylinder;
• a rod string that is mechanically connected to and that extends downwardly from the polished rod, the rod string being configured to extend into the wellbore;
• a positive displacement pump disposed at a lower end of the rod string, the positive displacement pump being configured to pump formation fluids up the wellbore in response to reciprocal motion of the rod string;
• a high pressure gas tank;
• a compressor configured to pump a working gas into the cylinder as part of a closed loop pumping system, wherein the closed loop pumping system comprises the high pressure gas tank and one or more low pressure gas tanks, such that the working gas is pumped:
• from the compressor and into the high pressure gas tank,
• from the high pressure gas tank and into the cylinder disposed over the wellbore, thereby causing an upstroke of the piston and the operatively connected pump,
• on a downstroke of the piston rod and the operatively connected pump, from the cylinder to the one or more low pressure gas tanks, and
• from the one or more low pressure gas tanks back to the compressor;
• a position sensor disposed along the cylinder to sense a vertical position of the piston within the cylinder in real time;
• a pressure transducer configured to sense pressure within the cylinder in real time;
• and
• a controller configured to receive signals from the position sensor and the pressure transducer, and from those signals adjust upstroke speed, downstroke speed, or both, of the piston within the cylinder.