Self-adjusting centralizer

Abstract

An oil-field tool for use in combination with a MWD tool, for deployment and retrieval of a MWD tool through a drill string, and, for rigid continuously self-adjusting, centralization of the MWD tool during drilling, includes: housing having a tapering nose; slidable shaft having a flared portion; extendable fingers pivotably attached to the slidable shaft; means for releasable attachment to a workstring; and, means for attachment to a MWD tool. Typically, the housing of the invention is attached to a MWD tool while at the surface and the combined apparatus is lowered through the drill string by wireline releasably attached to the slidable shaft. During lowering, the weight of the housing and MWD tool extends the slidable shaft, positioning the extendable fingers above the tapering nose of the housing, thereby retracting the fingers. When the MWD tool lodges downhole, the slidable shaft moves downward, causing the fingers to override the tapering nose of the housing and extend the fingers outward against the drill pipe. During drilling operations mud flowing through the drill pipe acts downwardly on flared portion of the slidable shaft inducing more forceable extension of the fingers against the drill pipe, maintaining rigid centralization of the MWD. Retrieval of the MWD is typically had by interrupting mud flow and lifting of the self-adjusting centralizer through the drill string by wireline.