Filtering media for controlling the flow of sand during oil well operations

A filter assembly for use in filtering sand from oil flow from a sand-containing oil producing formation or interval of an oil well, said filter assembly comprising a perforated pipe member, an outer annular wire mesh screen surrounding the pipe member, an inner wire mesh screen extending longitudinally within the pipe member, said outer and inner annular screens defining an annular chamber within which the perforated pipe member is located, said annular chamber containing filtering media comprising a body of juxtaposed composite particles smaller than the performations in the pipe member and retained in place by the screens, each composite particle having an iron-containing core surrounded by a continuous chromium cladding, said composite particles having a size to permit passage of the oil flow through the body of the composite particles while substantially preventing flow of sand therethrough, said composite particles being substantially spherical with a diameter in the range of from about 250 to about 2000 micrometers, the chromium cladding of each composite particle having a thickness in the range of from about 4 to about 30 micrometers, and said iron-containing core of each composite particle containing from about 0.8 to about 1.2% by weight carbon.

A composite particle comprising an iron-containing core surrounded by a continuous chromium cladding, the particle having a diameter in the range of from about 250 to about 2000 micrometers, the chromium cladding having a thickness in the range of from about 4 to about 30 micrometers, and said iron-containing core containing from about 0.8 to about 1.2% by weight carbon.