1. A system for collaboratively managing oilfield operations for an oilfield having geological formations and reservoirs therein, comprising: a network; a workflow server connected to the network, the workflow server configured to execute a workflow manager comprising functionality to: present, to a user, a graphical user interface (GUI) configured to generate a workflow for performing oilfield operations, wherein the GUI comprises a workflow diagram panel; receive a plurality of work steps selected by the user; generate, in the workflow diagram panel, a workflow diagram interconnecting the plurality of work steps; receive activation from the user to execute the workflow; receive, in the workflow diagram panel and during execution of the workflow, contact information for one or more other users from the user for a work step of the plurality of work steps; send, using the contact information and in response to execution of the workflow reaching the work step, a request to the one or more other users to provide input for the work step along with information needed to access the work step, including a Uniform Resource Locator (URL); receive the input from the one or more other users to add another work step in the workflow diagram panel; lock, in response to the input, the workflow for modification by the one or more other users while adding the another work step to the workflow; and inform the user of changes made by the one or more other users; and a plurality of computers configured to connect to the workflow server over the network and configured to: access the workflow manager and the workflow.