Summary To investigate the causes of fluid migration behind the casing after primary cementing, pressure and temperature measurements were made in the annulus of seven wells during cementing operations. Sensors were attached to the outside of the casing as it was run into each well; in this way data were obtained from several depths. A logging cable, also clamped to the casing, was used to bring data from the sensors to the surface. In some of the wells these annular measurements were continued during subsequent completion or work over operations. The pressure data could be used to determine conditions that either prevented or allowed fluid entry into the wellbore. Generally, pressure in the cement column began to decrease shortly after the cement was pumped. The success of the cementing operation depended on the cement attaining sufficient strength to exclude pore fluids from the cement before the pressure somewhere in the cement column declined to pore pressure at that depth. Pressure in the cement generally appeared to decline to the pore pressure in adjacent formations after the cement had set. In one well, however, pressure in the cement opposite a "tight streak" steadily declined to far less than a water hydrostatic gradient as the cement set. Fluid did not enter the wellbore and migrate to the surface soon after cementing in any of the wells investigated, but in one well fluid flow between zones behind the casing was indicated when the pressure in the cement decreased to pore pressure before the cement set. Before perforating was performed, annular flow was confirmed by a noise log in this well. The pressure sensors allowed other observations to be made both during and after cementing, including the effects of annular pressure applied at the surface during curing of the cement, and communication behind the casing during perforating, acidizing, and squeeze cementing. The temperature measurements in the annulus were used to monitor the setting of the cement, which is accompanied by evolution of heat. The cement generally set from the bottom of the wellbore toward the top. These field data confirm laboratory data that show a pressure decline in a cement column as the cement cures. pressure decline in a cement column as the cement cures. Conditions more likely to lead to annular fluid migration before the cement sets and steps that can be taken to decrease the likelihood of these occurrences can be identified from the field results. The pressure loss in a cement column before the cement cures is believed frequently to be responsible for vertical fluid flow behind the casing. The acronym FILAP is suggested for the phenomenon of "flow induced by loss in annular phenomenon of "flow induced by loss in annular pressure." pressure." Introduction The importance of achieving successful primary cementing of a well is hard to overemphasize. If there is a failure to seal the annulus outside the casing or liner, pressure may appear at the surface of the well from pressure may appear at the surface of the well from migrating gas (which is called "annular gas flow"), a liner top may leak, or fluids may flow between zones behind the casing in the well. Flow between zones can cause the loss of valuable hydrocarbons, the failure of stimulation treatments, and other problems. JPT P. 1429
Summary Pressure and temperature measurements were made in the Pressure and temperature measurements were made in the annulus of wells with sensors placed on the casings as they were run into the wells. The primary purpose of these measurements was to study the phenomenon of pressure reduction in the cement as it cures. This aspect of the measurements was reported in Ref. 1. Other phenomena were observed during these measurements, however, which are important to the cementing of a well and to casing design. This paper discusses three such phenomena: temperature in the annulus during cementing, loss of returns during cementing, and long-term pressure decline in a mud column above cement. The industry has made several studies over the years to improve the prediction of temperature of cement during pumping. The predictions of bottomhole circulating temperature (BHCT) from an extensive API study agree well with measured data in three of the five wells discussed in this paper. However, better predictions of cementing temperature in all five wells were obtained with a numerical method. The phenomenon of loss of returns during cementing can be very complex. Pressures in the cement during pumping may be greater than expected because the pumping may be greater than expected because the cement is rising more than anticipated (because of bypassing of mud) or for other reasons. The resistance of the wellbore to hydraulic fracturing and consequent loss of returns is difficult to predict accurately. The behavior in two wells is described. Casing design requires assumptions about the pressure behind the casing to calculate internal burst pressure. The data available from two wells indicate that hydrostatic pressure exerted by mud left in the annulus above cement pressure exerted by mud left in the annulus above cement decreases with time, and original mud weights should not be used as the backup pressure in casing burst design. Introduction Results of pressure and temperature measurements made in the annulus of wells during and after cementing operations were reported in Ref. 1. That paper focused on the importance of pressure decline in the cement column in the time interval after the cement is pumped and before the cement has cured. Observations regarding remedial cementing and acidizing treatments were reported also. The procedures and equipment used in those measurements were described and are not repeated in detail in this paper. This paper provides comparisons of measured and predicted BHCT's during cementing. The predicted predicted BHCT's during cementing. The predicted temperatures were developed from two sources: an API publication and a numerical calculation. An API task publication and a numerical calculation. An API task group provided very valuable data for predicting BHCT. The API correlation is now a part of Ref. 3. (The same data were provided in the preceding API document, RP 10B, which was superseded.) These data were collected from 78 wells in 10 states, at depths of 4,000 to 23,000 ft [1219 to 7010 m]. Numerical procedures for predicting downhole temperature during cementing also have predicting downhole temperature during cementing also have been developed over the years, the most recent being that by Wooley. This paper provides references to many earlier papers. Here, we compare measured temperatures to those predicted by the numerical method described by Sump and Williams. This numerical model was developed by fitting 28 unsteady-state circulating temperature measurements made in nine wells to derive heat transfer coefficients and effective formation thermal conductivities. The second topic concerns cementing of lost return zones (or lost circulation zones), a long-standing problem. Loss of returns often will occur during problem. Loss of returns often will occur during cementing even though the problem did not occur during drilling. Usual steps to solve the problem include the use of granular or fibrous materials in the cement or preflushes of material designed to form a precipitate and plug the channels or the fracture where returns are lost. The mechanism by which loss of returns occurs in some formations is not well understood, but in the examples in this paper the mechanism is believed to be hydraulic fracturing. A fracture is initiated when fluid pressures at the wellbore surface are greater than the tensile strength of the rock plus the compressive earth stress at the wellbore at some depth. The fluid pressure required to initiate a fracture is usually higher than the pressure required to open a preexisting natural or induced fracture or to propagate a fracture after it is formed. propagate a fracture after it is formed. The third topic discussed in this paper is the long-term decrease in hydrostatic pressure exerted by the mud column above the cement. JPT P. 2181
Papua New Guinea is a country in the South Pacific with a population of 6.7 million. Residents speak over 800 languages and live in a primarily rural agrarian society considered to be one of the world's biodiversity hotspots. Into this framework, Esso Highlands Limited, an affiliate of ExxonMobil Corporation is developing the USD $15.7 billion PNG LNG Project ("Project") and has realized considerable success in the implementation of a site specific process for identification and management of environmental, cultural, and social issues as a supplemental process to the Project's original Environmental Impact Statement. This site specific process was implemented to ensure timely Government approval of the Project's Environment Permit in order to meet the Final Investment Decision (FID) schedule, and to meet internal and external stakeholder expectations. This process required the completion of a P re-Construction Survey which provides a high quality assessment and review of environmental and social (E&S) issues at a local level and details the specific mitigation measures that are required to be implemented at a particular location. Overall, this process drives environmental and social performance at the field level by identifying very specific issues at individual worksites/locations for appropriate management while shifting some of the environmental assessment aspects from the pre-planning phase to the execution/construction phase. To date over 100 P re-Construction Surveys have been completed through a significant effort by the Project with great results. Ecological and cultural heritage features were identified and subsequently avoided and managed through site specific measures. Priority weeds and pests were identified for surveillance and control. Regulator acceptance of the surveys was obtained in a timely fashion thereby supporting the Project execution schedule. Overall, this approach supported the FID execution schedule for the Project with successful issuance of the Project's Environment Permit in early 4Q 2009 and allowed associated costs for the site specific approach to occur following the FID. It also enabled the Project to focus resources on the site specific examination/identification of environmental sensitivities to coincide with the Project's execution schedule.
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