A poly-L-lactic acid (PLLA) solid-state extrusion molded article having a weight average molecular weight of from 100,000 to 380,000 and a melt viscosity of from 20 to 2,000 Pa·s (at a temperature of 240° C. and a shear rate of 120 sec−1) and having an L-form content of from 80 to 100%, the article having a thickness or diameter of from 10 to 500 mm and a tensile strength of from 5 to 100 MPa at a temperature of 66° C. (the article may contain a filler and have a tensile strength of from 5 to 200 MPa); a downhole tool member or a ball sealer for well drilling and completion formed by machining the solid-state extrusion molded article; an isolation plug provided with the downhole tool member; and a production method for a PLLA solid-state extrusion molded article comprising steps of supplying a resin material containing a PLLA to an extruder, solid-state extrusion molding the material, pressurizing the solid-state extrusion molded product, drawing the pressurized product while applying a back pressure in the direction of a forming die to suppress the expansion of the solid-state extrusion molded product; and a well drilling and completion method.