An Example from the Cantarell Oilfield, Gulf of Mexico Geofísica Internacional, Vol

Geofísica Internacional ISSN: 0016-7169 [email protected] Universidad Nacional Autónoma de México México Shunshan, Xu; Nieto-Samaniego, Ángel Francisco; Velasquillo-Martínez, Luis Germán; Grajales- Nishimura, José Manuel; Murillo-Muñetón, Gustavo; García-Hernández, Jesús Factors influencing the fault displacement-length relationship: an example from the Cantarell oilfield, Gulf of Mexico Geofísica Internacional, vol. 50, núm. 3, julio-septiembre, 2011, pp. 279-293 Universidad Nacional Autónoma de México Distrito Federal, México Available in: http://www.redalyc.org/articulo.oa?id=56820212003 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative GEOFÍSICA INTERNACIONAL (2011) 50-3: 279-293 ORIGINAL PAPER Factors influencing the fault displacement-length relationship: an example from the Cantarell oilfield, Gulf of Mexico Xu Shunshan*, Ángel Francisco Nieto-Samaniego, Luis Germán Velasquillo-Martínez, José Manuel Grajales-Nishimura, Gustavo Murillo-Muñetón and Jesús García-Hernández Received: June 24, 2010; accepted: March 9, 2011; published on line: June 30, 2011 Resumen Abstract Asumiendo que la relación entre máxima Assuming a linear relationship between maximum longitud y máximo desplazamiento en las fallas length (L) and maximum fault displacement es lineal, investigamos los efectos de considerar (D) we investigate the effects of displacement distintos componentes del desplazamiento, del component measured, observation level, and nivel de observación, y la presencia de enlace fault linkage by using data from the normal de fallas. Para ello usamos datos de las fallas faults of the Akal block of the Cantarell oilfield normales del bloque Akal, en el campo petrolero in the southern Gulf of Mexico (off Campeche). de Cantarell, localizado en el Golfo de México The data are measured from structural contour frente a las costas de Campeche. Los datos maps at four different horizons. The summarized que se utilizaron fueron tomados de mapas de results are: (1) dip displacement is better contornos de cuatro horizontes diferentes. Los than vertical displacement to analyze the D-L resultados obtenidos pueden resumirse de la relationship; (2) data from two-tip faults produce 2 manera siguiente: (1) el desplazamiento al higher correlation coefficients (RL ) for linear echado es mejor que el desplazamiento vertical regression between D and L than one-tip faults; 2 para el análisis de la relación D-L; (2) utilizando (3) The correlation coefficients (RL ) are different fallas que muestran sus dos terminaciones se for each analyzed horizons, suggesting that the 2 logran mejores coeficientes de correlación lineal value of RL is dependent on the observed level. entre D y L, que utilizando fallas con una sola o ninguna terminación; (3) los coeficientes de Key words: fault, displacement, length, sampling, 2 correlación (RL ) obtenidos para las gráficas D-L linkage, Mexico. en cada horizonte son distintos, lo que indica que 2 los valores de (RL ) son dependientes del nivel de observación. Palabras clave: falla, desplazamiento de falla, longitud de falla, enlace de falla, México. Xu Shunshan* J. M. Grajales-Nishimura Centro de Geociencias Instituto Mexicano del Petróleo Universidad Nacional Autónoma de México Eje Central Lázaro Cárdenas No. 152 Apartado Postal 1-742, 76001 Col. San Bartolo Atepehuacan, 07730, Querétaro, Qro., México. México D.F., México. *Corresponding author:[email protected] G. Murillo-Muñetón A. F. Nieto-Samaniego Instituto Mexicano del Petróleo Centro de Geociencias Eje Central Lázaro Cárdenas No. 152 Universidad Nacional Autónoma de México Col. San Bartolo Atepehuacan, 07730, Apartado Postal 1-742, 76001 México D.F., México. Querétaro, Qro., México. J. García-Hernández L.G. Velasquillo-Martínez Petróleos Mexicanos Exploración Instituto Mexicano del Petróleo y Producción Región Marina NE, Eje Central Lázaro Cárdenas No. 152 Activo Cantarell (PEP-RMNE). Col. San Bartolo Atepehuacan, 07730, México D.F., México. 279 X. Shushan et al. Introduction first stage the gradient of D is than that of L, at second stage (part B in Figure 1a) the gradient The relationship between the maximum displa- of D is nearly equal to that for L, whereas at cement (D) and fault length (L) of faults is the final stage the gradient of increase for D is commonly written as a power law: higher than that for L (Figure 1a). The objective of this paper is to investigate D = cLn , (1) how sampling influences the measured fault parameters, in order to determine better where c is a constant related to material sampling conditions. The fault plane is properties. Whether a universal value of n exists considered to have elliptical shape (Walsh and is a debated issue. The published values of n range Watterson, 1987). The dimension along the slip from 0.5 to 2.0 (e.g. Watterson, 1986; Walsh direction is shorter than that nomal to the slip and Watterson, 1988; Marrett and Allmendinger, direction (Figures 1b, 1c, 1d). Thus, for normal 1991; Bonnet et al., 2001; Mazzoli et al., 2005). and reverse faults, the dip dimension is shorter Published data show that the relationship of than the strike dimension (Figures 1b, 1c). For maximum displacement to fault trace length is strike-slip faults, the strike dimension is longer linear for tectonic environments with uniform than the dip dimension (Figure 1d). In our study mechanical properties (Cowie and Scholz, 1992; area, the faults are normal faults similar to the Dawers et al., 1993; Xu et al., 1998; Xu et al., ellipse in Figure 1b. For simplicity we assume 2006; Schultz et al., 2008). Many researchers that n = 1, and we analyze an example from accept that n = 1 on that condition. the Cantarell oilfield in the southern Gulf of Mexico. The parameters considered in the study The value of n is important for explaining the area were fault displacement components, fault mechanism of fault growth and in a more practical interaction, and observation level. sense, for estimating D from measurements of L or vice versa. For a given value of n, both Geological background maximum displacement and length increase with fault growth (Figure 1a). However, the gradients The Cantarell oilfield is located in the Gulf are different depending on the value of n. For n = of Mexico, in the southern part of the North 1, the rate of increase for both D and L remains American Plate (Fig. 2a). The tectonics of the constant during the growth of the fault. For n Gulf of Mexico is controlled by the interactions of < 1, at the initial stage (part A in Figure 1a), the Caribbean, North America and Cocos plates the gradient of D is steeper than that of L, at a at least for the last 74 Ma (Whitman et al., 1983). higher stage (part B in Figure 1a) the gradient The Middle America trench marks the location of of D is nearly equal to that of L, and in the final north-eastward subduction of the Cocos plate stage (part C in Figure 1a), the gradient of D is under the North American and Caribbean plates smaller than that of L. Similarly, for n > 1, at (LeFevre and McNally, 1985). In Campeche Figure 1. (a) Growth trend of fault from equation D = cLn. The arrow indicates the growth direction. (b), (c), and (d) illustrate the fault shape for normal fault, reverse fault and strike-slip fault, respectively. The arrow indicates slip direction. 280 VOLUME 50 NUMBER 3 GEOFÍSICA INTERNACIONAL Bay (Figure 2) three main superimposed Similarly, three main episodes of deformation tectonic regimes are recorded: extensional, occurred in the Cantarell oilfield (Mitra et al., compressional, and extensional (Angeles-Aquino 2005). First, extension during Jurassic to Early et al., 1994). The first period initiated in Middle Cretaceous produced normal faults that mainly Jurassic, and is related to the opening of the Gulf affected Tithonian, Kimmeridgian, and Lower of Mexico. During this regime NW-SE faulting Cretaceous units. Second, compression in was dominant. The subsequent compressional Miocene produced the NW trending Cantarell regime took place in Middle Miocene. It was thrust system. The Sihil thrust fault separates the related to a northeast principal stress which allochthonous and autochthonous blocks (Figures often formed overturned anticlines. The last 2b, 2c). Third, there was Pliocene to Holocene extensional regime extended through Middle and extension; during this phase of deformation Late Miocene and has a Middle Miocene shaly several preexisting Jurassic normal faults were horizon as detachment surface. During the last reactivated and new NS to NW trending normal two regimes a salt tectonics occurred in the faults were formed. The structural style in the area, overprinting structures and disturbing the Cantarell complex has been shaped by three regional stress field. major tectonic phases. The Akal anticline is a Figure 2. (a) Simplified plate map showing the location of the Gulf of Mexico and Cantarell oilfield. (b) Structural sketch of Cantarell oilfield. (c) Typical cross section in the studied area. (d) Integrated stratigraphic column of the Cantarell oilfield. JULY - SEPTEMBER 2011 281 X. Shushan et al. structure associated with the reverse fault belt. anticline is about 300˚NW. The fold is a SE- The anticline trends SE-NW and slightly plunges plunging fold. The angle between limbs of the to southeast. The interpreted seismic section fold is intermediate. The faults in the Akal block shows that the northeastern limb of Akal anticline are normal faults, but the observed slickenside is steeper than the southwestern limb (Aquino- striations in minor faults from core samples are Lopez, 1999). generally not along the fault dips (Xu et al., 2004), implying that the faults have a strike component We select the Akal block of the Cantarell of displacement. Based on the evident strike oilfield in the southern Gulf of Mexico (offshore component of displacement on fault planes, Campeche) as a case study (Figure 2b).

Load more