A method of installing a wellhead platform for exploring hydrocarbon below seabed which includes a wellhead deck and a sub-sea conductor frame using an offshore unit (10, 60, 62, 64, 58, 70) which includes: - a hull and/or a deck frame; - a mat attached to at least one connecting leg or a spud can attached to each of at least one connecting leg or a lower hull; wherein the method includes the following steps: i) transporting the offshore unit (10, 60, 62, 64, 58, 70) to an offshore installation site; ii) installing the offshore unit (10, 60, 62, 64, 58, 70); iii) deploying means for exploring hydrocarbon below seabed supported by the wellhead deck until the means for exploring hydrocarbon below seabed penetrate through soil layers to target penetration; iv) retrieving the means for exploring hydrocarbon; v) installing at least one conductor through the wellhead deck and the sub-sea conductor frame until the at least one conductor penetrates through soil layers to target penetration; vi) securing the wellhead deck to the at least one conductor; and wherein the wellhead deck is removably attached to the hull and/or the deck frame; and wherein the sub-sea conductor frame is removably attached to the mat or to the at least one connecting leg, wherein a spud can is attached to each of at least one connecting leg, or to the lower hull; and wherein the wellhead deck and the sub-sea conductor frame are attached to the offshore unit (10, 60, 62, 64, 58, 70) prior to loading out and transporting the platform from fabrication site to the offshore installation site; and wherein the hull and/or the deck frame and the mat or the spud can are connectable with the at least one connecting leg; and wherein the hull and/or the deck frame and the lower hull are connectable with the at least one connecting means. - a hull and/or a deck frame; - a mat attached to at least one connecting leg or a spud can attached to each of at least one connecting leg or a lower hull; wherein the method includes the following steps: i) transporting the offshore unit (10, 60, 62, 64, 58, 70) to an offshore installation site; ii) installing the offshore unit (10, 60, 62, 64, 58, 70); iii) deploying means for exploring hydrocarbon below seabed supported by the wellhead deck until the means for exploring hydrocarbon below seabed penetrate through soil layers to target penetration; iv) retrieving the means for exploring hydrocarbon; v) installing at least one conductor through the wellhead deck and the sub-sea conductor frame until the at least one conductor penetrates through soil layers to target penetration; vi) securing the wellhead deck to the at least one conductor; and wherein the wellhead deck is removably attached to the hull and/or the deck frame; and wherein the sub-sea conductor frame is removably attached to the mat or to the at least one connecting leg, wherein a spud can is attached to each of at least one connecting leg, or to the lower hull; and wherein the wellhead deck and the sub-sea conductor frame are attached to the offshore unit (10, 60, 62, 64, 58, 70) prior to loading out and transporting the platform from fabrication site to the offshore installation site; and wherein the hull and/or the deck frame and the mat or the spud can are connectable with the at least one connecting leg; and wherein the hull and/or the deck frame and the lower hull are connectable with the at least one connecting means. i) transporting the offshore unit (10, 60, 62, 64, 58, 70) to an offshore installation site; ii) installing the offshore unit (10, 60, 62, 64, 58, 70); iii) deploying means for exploring hydrocarbon below seabed supported by the wellhead deck until the means for exploring hydrocarbon below seabed penetrate through soil layers to target penetration; iv) retrieving the means for exploring hydrocarbon; v) installing at least one conductor through the wellhead deck and the sub-sea conductor frame until the at least one conductor penetrates through soil layers to target penetration; vi) securing the wellhead deck to the at least one conductor; and wherein the wellhead deck is removably attached to the hull and/or the deck frame; and