Subsea Pipeline Crossings in the Cantarell Field, Bay of Campeche, Mexico
Authors: Diri C.M. , Speirs A.P. , Khoury T.C. , Reichard R.H. , Laskar P.R. 
Published: October 2008

Abstract
Approximately fifty new submarine pipelines are currently being added to the eighty existing pipelines within the Cantarell Field. When all pipelines are complete, there will be approximately two hundred new pipeline crossings. The existing pipelines, many of which are exposed on the seabed, must continue to service during new pipeline crossing installations. As the new pipelines are required to be buried with 1m cover, the preferred crossing method required lowering the existing pipeline into the seabed. This paper reviews the design approach, crossing types selected and construction methods for safely crossing types selected and constructions methods for safely crossing the existing operating pipelines. With limited as-built information available, on site survey conservative assumptions and reverse engineering were required.

Introduction
Pemex is undertaking a major upgrade and expansion of the Cantarell oil field in the Gulf of Mexico in order to curtail gas flaring, increase crude oil production and exports, and to improve the reliability of existing facilities.
The bulk of Cantarell pipeline construction work was completed between 1977 and 1982. Some additional pipelines were constructed later, including a gas list distribution system which was completed in 1987. Altogether, the existing subsea pipelines connecting the Cantarell facilities number more than 80.
Since Pemex Exploration and Production (PEP) awarded Bechtel a contract for field development planning and overall program management in late 1996, contracts have been awarded for the engineering, procurement and construction of over 50 new submarine pipelines. When all pipelines are complete, there will be approximately 200 new pipeline crossings.
This paper reviews the design approach and construction methods developed to safely cross existing operating pipelines with new pipelines, without interrupting oil and gas production, and minimizing the risk to PEP facilities and operating personnel. The integrity of the existing pipelines is maintained by keeping a safe limit on stress. With limites information available on the existing pipelines, onsite surveys, conservative assumptions and reverse engineering were required.

Crossings
Several crossing types were identified and have been installed in the current pipeline work:Lowered crossingBridge crossingLayover crossingCombination crossingFuture crossing
The crossing type that is highlighted in this paper is the "lowered crossing", because it involved the intentional relocation of existing, operating, pressurized subsea oil and gas pipelines, some in service over twenty years. This method is preferred by PEP as it adheres to its requirement that all new pipelines in Cantarell have 1 meter cover. A conservative design criteria and method of crossing analysis to minimize risk was established as damage to an operating pipeline could not be tolerated.

Lowered Crossing.
As the seabed in the Cantarell field is generally composed of sandy clay materials that can be jetted for pipe burial, the goal was to specify both 1m cover and 1m separation between pipelines at all crossings accessible to a barge-towed jet sled.