Offshore Surveying

This paper was prepared for the 41st Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Dallas, Tex., Oct 2–5, 1966. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers Office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines. Introduction This paper will be limited to offshore surveying as it is conducted off the coast of Louisiana. California and Texas use the same mapping systems, but the arrangement and size of the blocks vary slightly. THEORIES AND DEFINITIONS Surveying on the open water employes a slightly different technic to that used on land. First, it is impossible to use a tape or chain to measure distances, therefore electronic measuring devices are used. Second, the distances being greater from known points; a more precise instrument for turning directions is used. One advantage in offshore surveying is the designation of property lines. Onshore the corners of Townships, Ranges, and Section Corners are marked by material objects such as: iron posts, rock mounds, wooden stakes, trees, and others. Offshore the Area and Block Corners are given a precise Geographic Position expressed as Lambert Coordinates. The maps showing the boundaries of offshore leases are constructed on the Lambert Conformal Conic Projection. This map projection was conceived and constructed by Johann Heinrick Lambert, a German Physicist, Mathematician, and Astronomer, in the year 1772. The Lambert Conformal Conic Projection is of the simple conical type, in which all meridians are straight lines that meet in a common point beyond the limits of the map, and the parallels are concentric circles whose center is at the point of intersection of the meridians. Meridians and parallels interact at right angles, and the angle formed by any two lines on the earths' surface are correctly represented on this projection. This projection employs a cone intersecting the spheroid at two parallels, known as the standard parallels for the area to be represented. In general, for equal distribution of scale error, the standard parallels are chosen at one-sixth and five-sixth of the total length of that portion of the central meridian to be represented. On the two selected parallels, arcs of longitude are represented in their true lengths, or to exact scale. Between these parallels the scale will be too small and beyond them too large. The reason for the scale factor change is the projection of the curved surface of the sphere on to the pane. This projection is specially suited for maps having a predominating east and west dimension. The chief advantage of this projection over the poloconic, is the reduction of the scale error from 7% in the poloconic to 2 1/2% in the lambert. The South Zone of Louisiana was constructed using 91 degrees 20' 00" and 29 degrees 18' and 30 degrees 42' North Latitude as the standard parallels.